[llvm] [PowerPC] Implement Elliptic Curve Cryptography (ECC) Instructions (PR #158362)

[Maryam Moghadas via llvm-commits]

maryammo wrote:

These instructions listed in the PR description appear to be missing from the implementation: 
`xsaddsubuqm`, `xsaddsubsuqm`

https://github.com/llvm/llvm-project/pull/158362