[feature] Load a TVM from an ELF

[alarmfox]

Description

This PR improves the TSM so that we can load an elf as a VM. The elf loading is performed by the untrusted OS which maps pages into the trusted partition (managed by the TSM). This example can be performed using the gdb_covh_create_tvm_from_elf-py.

The TVM cannot interacts with any external device, but it can be some code like:

    .section .text
_start:
    /* Reset registers */
    mv ra, zero
    mv gp, zero
    mv tp, zero
    mv t0, zero
    mv t1, zero
    mv t2, zero
    mv s0, zero
    mv s1, zero
    mv a0, zero
    mv a1, zero
    mv a2, zero
    mv a3, zero
    mv a4, zero
    mv a5, zero
    mv a6, zero
    mv a7, zero
    mv s2, zero
    mv s3, zero
    mv s4, zero
    mv s5, zero
    mv s6, zero
    mv s7, zero
    mv s8, zero
    mv s9, zero
    mv s10, zero
    mv s11, zero
    mv t3, zero
    mv t4, zero
    mv t5, zero
    mv t6, zero

    /* Hang */
1:  j 1b

Which can be compiled with:

/riscv64-unknown-linux-gnu-gcc -nostdlib -nostartfiles -Wl,-Ttext=0x1000 a.S

Other changes

• Remove environment.sh and export variable from Makefile
• Update documentation on how to run examples
• Easy debug examples with make debug GDB_COVE_SCRIPT=<path to script>
• Computing SHA384 for TVM data in measured pages
• Updated Dockerfile and improved build-system