[llvm] [Hexagon] Add missing patterns to select PFALSE and PTRUE (PR #138712)

[via llvm-commits]

dyung wrote:

> I also agree with a backport of the test case fix into the release/20.x branch.
> 
> /cherry-pick [194a4a3](https://github.com/llvm/llvm-project/commit/194a4a333a95f9e001d2c8abe82c3d4cf8894acf)

FYI, I've already requested it to be ported to the release branch at https://github.com/llvm/llvm-project/pull/139822. It is just awaiting merging.

https://github.com/llvm/llvm-project/pull/138712