[llvm] Split vgpr regalloc pipeline (PR #93526)

[Christudasan Devadasan via llvm-commits]

cdevadas wrote:

This patch would replace the PR https://github.com/llvm/llvm-project/pull/86012. The two generic features introduced earlier were strongly discouraged. This patch splits the VGPR allocation further to handle the wwm-allocation in a target-specific way.

https://github.com/llvm/llvm-project/pull/93526