[AMDGPU] Add test for v_fmamk_f16/v_fmaak_f16 in real-true16. NFC

This is to display a bug in real true16 mode that we do not have
an allocatable 16-bit VGPR class and these instructions do not
have VOP3 forms for allocatable VGPR_16 to be used. To use these
instructions 'VGPR_16_Lo128' must be allocable.

Author: rampitec

llvm/test/CodeGen/AMDGPU/fmamk_fmaak-t16.mir

@@ -0,0 +1,31 @@
+# RUN: not llc -mtriple=amdgcn -mcpu=gfx1100 -mattr=+real-true16 -run-pass=machineverifier -filetype=null %s 2>&1 | FileCheck %s -check-prefix=GFX11
+# RUN: not llc -mtriple=amdgcn -mcpu=gfx1100 -mattr=+real-true16 -start-before=greedy,0 -stop-after=virtregrewriter,2 -o - %s 2>&1 | FileCheck %s -check-prefix=GFX11
+
+# FIXME: There is no allocatable 16-bit VGPR class and these instructions
+#        do not have VOP3 forms for allocatable VGPR_16 to be used.
+
+# GFX11: Cannot use non-allocatable class 'VGPR_16_Lo128' for virtual register
+
+---
+name:            v_fmamk_f16
+tracksRegLiveness: true
+body:             |
+  bb.0:
+    liveins: $vgpr0, $vgpr1
+    %0:vgpr_32_lo128 = COPY $vgpr0
+    %1:vgpr_32_lo128 = COPY $vgpr1
+    %2:vgpr_16_lo128 = nofpexcept V_FMAMK_F16_t16 %0.sub0, 1, %1.sub1, implicit $exec, implicit $mode
+    S_ENDPGM 0, implicit %2
+...
+
+---
+name:            v_fmaak_f16
+tracksRegLiveness: true
+body:             |
+  bb.0:
+    liveins: $vgpr0, $vgpr1
+    %0:vgpr_32_lo128 = COPY $vgpr0
+    %1:vgpr_32_lo128 = COPY $vgpr1
+    %2:vgpr_16_lo128 = nofpexcept V_FMAAK_F16_t16 %0.sub0, %1.sub1, 1, implicit $exec, implicit $mode
+    S_ENDPGM 0, implicit %2
+...