[llvm] [AMDGPU][GlobalISel] Add register bank legalization for buffer_load byte and short (PR #167798)

[LLVM Continuous Integration via llvm-commits]

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `ml-opt-dev-x86-64` running on `ml-opt-dev-x86-64-b2` while building `llvm` at step 6 "test-build-unified-tree-check-all".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/137/builds/30567

<details>
<summary>Here is the relevant piece of the build log for the reference</summary>

```
Step 6 (test-build-unified-tree-check-all) failure: test (failure)
******************** TEST 'LLVM :: CodeGen/AMDGPU/GlobalISel/buffer-load-byte-short.ll' FAILED ********************
Exit Code: 1

Command Output (stdout):
--
# RUN: at line 2
/b/ml-opt-dev-x86-64-b1/build/bin/llc -mtriple=amdgcn-amd-amdhsa -global-isel -new-reg-bank-select -mcpu=gfx1200 < /b/ml-opt-dev-x86-64-b1/llvm-project/llvm/test/CodeGen/AMDGPU/GlobalISel/buffer-load-byte-short.ll | /b/ml-opt-dev-x86-64-b1/build/bin/FileCheck --check-prefix=GFX12 /b/ml-opt-dev-x86-64-b1/llvm-project/llvm/test/CodeGen/AMDGPU/GlobalISel/buffer-load-byte-short.ll
# executed command: /b/ml-opt-dev-x86-64-b1/build/bin/llc -mtriple=amdgcn-amd-amdhsa -global-isel -new-reg-bank-select -mcpu=gfx1200
# executed command: /b/ml-opt-dev-x86-64-b1/build/bin/FileCheck --check-prefix=GFX12 /b/ml-opt-dev-x86-64-b1/llvm-project/llvm/test/CodeGen/AMDGPU/GlobalISel/buffer-load-byte-short.ll
# .---command stderr------------
# | /b/ml-opt-dev-x86-64-b1/llvm-project/llvm/test/CodeGen/AMDGPU/GlobalISel/buffer-load-byte-short.ll:160:15: error: GFX12-NEXT: expected string not found in input
# | ; GFX12-NEXT: s_wait_alu 0xf1ff
# |               ^
# | <stdin>:757:28: note: scanning from here
# |  v_readfirstlane_b32 s7, v3
# |                            ^
# | <stdin>:758:2: note: possible intended match here
# |  s_wait_alu depctr_va_sdst(0)
# |  ^
# | /b/ml-opt-dev-x86-64-b1/llvm-project/llvm/test/CodeGen/AMDGPU/GlobalISel/buffer-load-byte-short.ll:192:15: error: GFX12-NEXT: expected string not found in input
# | ; GFX12-NEXT: s_wait_alu 0xf1ff
# |               ^
# | <stdin>:864:23: note: scanning from here
# |  s_mov_b32 s7, exec_lo
# |                       ^
# | <stdin>:865:2: note: possible intended match here
# |  s_wait_alu depctr_va_sdst(0)
# |  ^
# | /b/ml-opt-dev-x86-64-b1/llvm-project/llvm/test/CodeGen/AMDGPU/GlobalISel/buffer-load-byte-short.ll:223:15: error: GFX12-NEXT: expected string not found in input
# | ; GFX12-NEXT: s_wait_alu 0xf1ff
# |               ^
# | <stdin>:970:28: note: scanning from here
# |  v_readfirstlane_b32 s9, v5
# |                            ^
# | <stdin>:971:2: note: possible intended match here
# |  s_wait_alu depctr_va_sdst(0)
# |  ^
# | 
# | Input file: <stdin>
# | Check file: /b/ml-opt-dev-x86-64-b1/llvm-project/llvm/test/CodeGen/AMDGPU/GlobalISel/buffer-load-byte-short.ll
# | 
# | -dump-input=help explains the following input dump.
# | 
# | Input was:
# | <<<<<<
# |             .
# |             .
# |             .
# |           752: .LBB8_1: ; =>This Inner Loop Header: Depth=1 
# |           753:  v_readfirstlane_b32 s4, v0 
...

```

</details>

https://github.com/llvm/llvm-project/pull/167798