[llvm] [X86] added computeKnownBits for X86ISD::GF2P8AFFINEQB (PR #194197)

[Simon Pilgrim via llvm-commits]

================

----------------
RKSimon wrote:

(style) avoid comments inside test code (it can mess with the update script) - but a BRIEF summary above the define line

https://github.com/llvm/llvm-project/pull/194197