[llvm] [TableGen] New tblgen Pattern bit to disable GISel pattern imports (PR #88382)

[Shilei Tian via llvm-commits]

https://github.com/shiltian commented:

LGTM with one nit. I'd wait to see if @arsenm and @Pierre-vh have more comments.

https://github.com/llvm/llvm-project/pull/88382