[llvm] [X86][MC] Support Enc/Dec for EGPR for promoted MOVDIR instruction (PR #74713)

[Shengchen Kan via llvm-commits]

================
@@ -0,0 +1,10 @@
+# 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
+
+# ATT:   movdir64b	291(%r28d,%r29d,4), %r18d
+# INTEL: movdir64b	r18d, zmmword ptr [r28d + 4*r29d + 291]
+0x67,0x62,0x8c,0x79,0x08,0xf8,0x94,0xac,0x23,0x01,0x00,0x00
----------------
KanRobert wrote:

`IC_EVEX_OPSIZE_ADSIZE` is still needed as we added `IC_ADSIZE`, `IC_64BIT_REXW_ADSIZE`.  Dropping the change in X86Disassembler.cpp may solve the problem since we already specially handle it.

@XinWang10 Please add test mentioned by Phoebe in a separate commit, like https://reviews.llvm.org/D122449 

@phoebewang `i512mem_GR32` is added for decoding issue only? This surprised me...  


https://github.com/llvm/llvm-project/pull/74713