[clang] [llvm] [AMDGPU] Add support for `v_cvt_pk_f16_bf8` on gfx1250 (PR #145753)

[LLVM Continuous Integration via cfe-commits]

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `clang-x86_64-debian-fast` running on `gribozavr4` while building `clang,llvm` at step 6 "test-build-unified-tree-check-all".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/56/builds/29343

<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 'Clang :: CodeGenOpenCL/builtins-amdgcn-gfx1250.cl' FAILED ********************
Exit Code: 2

Command Output (stderr):
--
/b/1/clang-x86_64-debian-fast/llvm.obj/bin/clang -cc1 -internal-isystem /b/1/clang-x86_64-debian-fast/llvm.obj/lib/clang/21/include -nostdsysteminc -cl-std=CL2.0 -O0 -triple amdgcn-unknown-unknown -target-cpu gfx1250 -emit-llvm -o - /b/1/clang-x86_64-debian-fast/llvm.src/clang/test/CodeGenOpenCL/builtins-amdgcn-gfx1250.cl | /b/1/clang-x86_64-debian-fast/llvm.obj/bin/FileCheck /b/1/clang-x86_64-debian-fast/llvm.src/clang/test/CodeGenOpenCL/builtins-amdgcn-gfx1250.cl # RUN: at line 2
+ /b/1/clang-x86_64-debian-fast/llvm.obj/bin/FileCheck /b/1/clang-x86_64-debian-fast/llvm.src/clang/test/CodeGenOpenCL/builtins-amdgcn-gfx1250.cl
+ /b/1/clang-x86_64-debian-fast/llvm.obj/bin/clang -cc1 -internal-isystem /b/1/clang-x86_64-debian-fast/llvm.obj/lib/clang/21/include -nostdsysteminc -cl-std=CL2.0 -O0 -triple amdgcn-unknown-unknown -target-cpu gfx1250 -emit-llvm -o - /b/1/clang-x86_64-debian-fast/llvm.src/clang/test/CodeGenOpenCL/builtins-amdgcn-gfx1250.cl
/b/1/clang-x86_64-debian-fast/llvm.src/clang/test/CodeGenOpenCL/builtins-amdgcn-gfx1250.cl:29:33: error: unknown type name 'half2'
   29 | void test_cvt_pk_f16_fp8(global half2* out, short a)
      |                                 ^
/b/1/clang-x86_64-debian-fast/llvm.src/clang/test/CodeGenOpenCL/builtins-amdgcn-gfx1250.cl:49:33: error: unknown type name 'half2'
   49 | void test_cvt_pk_f16_bf8(global half2* out, short a)
      |                                 ^
2 errors generated.
FileCheck error: '<stdin>' is empty.
FileCheck command line:  /b/1/clang-x86_64-debian-fast/llvm.obj/bin/FileCheck /b/1/clang-x86_64-debian-fast/llvm.src/clang/test/CodeGenOpenCL/builtins-amdgcn-gfx1250.cl

--

********************


```

</details>

https://github.com/llvm/llvm-project/pull/145753