[llvm] [X86] Correct the cdisp8 encoding for VGF2P8AFFINEINVQB and VGF2P8AFFINEQB. (PR #120340)

[Michael Clark via llvm-commits]

michaeljclark wrote:

larkmjc here. I was performing some differential fuzzing and checking word size with the broadcast cdisp8 multiplier. just to add to the notes. here are my exemplars from before the patch along with binutils output. these differ slightly from the test cases as they are using SIB and the ib is 0 instead of 7. I have checked this patch on my side but haven't run the tests in the test suite yet. thanks.

## llvm (18:18.1.3-1ubuntu1)
```
62 f3 fd 19 cf 44 51 01 00     vgf2p8affineinvqb	xmm0 {k1}, xmm0, qword ptr [rcx + 2*rdx + 1]{1to2}, 0
62 f3 fd 39 cf 44 51 01 00     vgf2p8affineinvqb	ymm0 {k1}, ymm0, qword ptr [rcx + 2*rdx + 1]{1to4}, 0
62 f3 fd 59 cf 44 51 01 00     vgf2p8affineinvqb	zmm0 {k1}, zmm0, qword ptr [rcx + 2*rdx + 1]{1to8}, 0
62 f3 fd 19 ce 44 51 01 00     vgf2p8affineqb	xmm0 {k1}, xmm0, qword ptr [rcx + 2*rdx + 1]{1to2}, 0
62 f3 fd 39 ce 44 51 01 00     vgf2p8affineqb	ymm0 {k1}, ymm0, qword ptr [rcx + 2*rdx + 1]{1to4}, 0
62 f3 fd 59 ce 44 51 01 00     vgf2p8affineqb	zmm0 {k1}, zmm0, qword ptr [rcx + 2*rdx + 1]{1to8}, 0
```
## binutils (2.42-4ubuntu2.3)
```
62 f3 fd 19 cf 44 51 01 00     vgf2p8affineinvqb xmm0{k1},xmm0,QWORD BCST [rcx+rdx*2+0x8],0x0
62 f3 fd 39 cf 44 51 01 00     vgf2p8affineinvqb ymm0{k1},ymm0,QWORD BCST [rcx+rdx*2+0x8],0x0
62 f3 fd 59 cf 44 51 01 00     vgf2p8affineinvqb zmm0{k1},zmm0,QWORD BCST [rcx+rdx*2+0x8],0x0
62 f3 fd 19 ce 44 51 01 00     vgf2p8affineqb xmm0{k1},xmm0,QWORD BCST [rcx+rdx*2+0x8],0x0
62 f3 fd 39 ce 44 51 01 00     vgf2p8affineqb ymm0{k1},ymm0,QWORD BCST [rcx+rdx*2+0x8],0x0
62 f3 fd 59 ce 44 51 01 00     vgf2p8affineqb zmm0{k1},zmm0,QWORD BCST [rcx+rdx*2+0x8],0x0
```

https://github.com/llvm/llvm-project/pull/120340