[llvm] [NFC][X86] Reorg MC tests for APX promoted instrs (PR #76697)

[Shengchen Kan via llvm-commits]

================
@@ -0,0 +1,226 @@
+# RUN: llvm-mc --disassemble %s -triple=x86_64 | FileCheck %s --check-prefixes=ATT
+# RUN: llvm-mc --disassemble %s -triple=x86_64 -x86-asm-syntax=intel --output-asm-variant=1 | FileCheck %s --check-prefixes=INTEL
+
----------------
KanRobert wrote:

Could you add comment like 
```
## mulx
```
when we start checking a new menonic ? This would improve the readability.

https://github.com/llvm/llvm-project/pull/76697