[llvm] [AArch64] Add USDOT to the instruction we perform performAddDotCombine. (PR #171864)

[Hari Limaye via llvm-commits]

https://github.com/hazzlim approved this pull request.

Nit: `s/instruction/instructions` in the commit message? Or perhaps `[AArch64] Support USDOT in performAddDotCombine` or similar?


Otherwise LGTM :) 

https://github.com/llvm/llvm-project/pull/171864