vendor-ibm-astlpc.md: Fix MD036 warnings

The following warnings are generated by using markdownlint analysis:
```
docs/bindings/vendor-ibm-astlpc.md:26 MD036/no-emphasis-as-heading Emphasis used instead of a heading [Context: "BTU: Baseline Transmission Uni..."]
docs/bindings/vendor-ibm-astlpc.md:31 MD036/no-emphasis-as-heading Emphasis used instead of a heading [Context: "IBF: Input Buffer Full"]
docs/bindings/vendor-ibm-astlpc.md:37 MD036/no-emphasis-as-heading Emphasis used instead of a heading [Context: "IDR: Input Data Register"]
docs/bindings/vendor-ibm-astlpc.md:42 MD036/no-emphasis-as-heading Emphasis used instead of a heading [Context: "KCS: Keyboard-Controller-Style"]
docs/bindings/vendor-ibm-astlpc.md:52 MD036/no-emphasis-as-heading Emphasis used instead of a heading [Context: "LPC Bus: Low Pin Count Bus"]
docs/bindings/vendor-ibm-astlpc.md:57 MD036/no-emphasis-as-heading Emphasis used instead of a heading [Context: "LPC FW: LPC Firmware Cycles"]
docs/bindings/vendor-ibm-astlpc.md:64 MD036/no-emphasis-as-heading Emphasis used instead of a heading [Context: "MTU: Maximum Transmission Unit"]
docs/bindings/vendor-ibm-astlpc.md:70 MD036/no-emphasis-as-heading Emphasis used instead of a heading [Context: "OBF: Output Buffer Full"]
docs/bindings/vendor-ibm-astlpc.md:76 MD036/no-emphasis-as-heading Emphasis used instead of a heading [Context: "ODR: Output Data Register"]
docs/bindings/vendor-ibm-astlpc.md:81 MD036/no-emphasis-as-heading Emphasis used instead of a heading [Context: "STR: Status Register"]
```
Refer to markdown-lint [1] to fix MD036
[1]: https://github.com/updownpress/markdown-lint/blob/master/rules/036-no-emphasis-as-header.md

Signed-off-by: George Liu <liuxiwei@ieisystem.com>
Change-Id: Id56964b7edff73c060215d27b55e558304b83269

Author: lxwinspur

docs/bindings/vendor-ibm-astlpc.md

@@ -23,23 +23,23 @@ document.
 
 ## Definitions
 
-**BTU: Baseline Transmission Unit**
+### BTU: Baseline Transmission Unit
 
 Defined by the MCTP base specification as the smallest maximum packet size all
 MCTP-compliant endpoints must accept.
 
-**IBF: Input Buffer Full**
+### IBF: Input Buffer Full
 
 A hardware-defined flag bit in a KCS device's Status Register (STR). The IBF
 flag indicates that a value has been written by the host to the corresponding
 Input Data Register (IDR).
 
-**IDR: Input Data Register**
+### IDR: Input Data Register
 
 One of the three register interfaces exposed by a KCS device. The IDR is a one
 byte buffer which is written by the host and read by the BMC.
 
-**KCS: Keyboard-Controller-Style**
+### KCS: Keyboard-Controller-Style
 
 A set of bit definitions and operation of the registers typically used in
 keyboard microcontrollers and embedded controllers. The term "Keyboard
@@ -49,36 +49,36 @@ systems. This interface is available built-in to several commercially available
 microcontrollers. Data is transferred across the KCS interface using a per-byte
 handshake.
 
-**LPC Bus: Low Pin Count Bus**
+### LPC Bus: Low Pin Count Bus
 
 A bus specification that implements ISA bus in a reduced physical form while
 extending ISA's capabilities.
 
-**LPC FW: LPC Firmware Cycles**
+### LPC FW: LPC Firmware Cycles
 
 LPC firmware cycles allow separate boot BIOS firmware memory cycles and
 application memory cycles with respect to the LPC bus. The ASPEED BMCs allow
 remapping of the LPC firmware cycles onto arbitrary regions of the BMC's
 physical address space, including RAM.
 
-**MTU: Maximum Transmission Unit**
+### MTU: Maximum Transmission Unit
 
 The largest payload the link will accept for a packet. The Maximum Transmission
 Unit represents a value that is at least as large as the BTU. Negotiation of MTU
 values larger than the BTU may improve throughput for data-intensive transfers.
 
-**OBF: Output Buffer Full**
+### OBF: Output Buffer Full
 
 A hardware-defined flag bit in a KCS device's Status Register (STR). The OBF
 flag indicates that a value has been written by the BMC to the corresponding
 Output Data Register (ODR).
 
-**ODR: Output Data Register**
+### ODR: Output Data Register
 
 One of the three register interfaces exposed by a KCS device. The ODR is a one
 byte buffer which is written by the BMC and read by the host.
 
-**STR: Status Register**
+### STR: Status Register
 
 One of the three register interfaces exposed by a KCS device. STR is a
 BMC-controlled, eight-bit register exposed to both the BMC and the host for