[llvm] AMDGPU: Use "countMaxActiveBits() <= 5" to define uint5Bits (PR #115543)

[Changpeng Fang via llvm-commits]

changpeng wrote:

> I think the whole original patch should be reverted

What is the original patch?  WE should not do pattern match for x << (32 -y) >> (32 - y)  to bfe x, 0, y?

https://github.com/llvm/llvm-project/pull/115543