[llvm] [AMDGPU] Add IR-level pass to rewrite away address space 7 (PR #77952)

[Krzysztof Drewniak via llvm-commits]

krzysz00 wrote:

This is the address space 7 work ported out from Phabricator, with changes made to reflect #77847 .

Landing this is annoyingly blocked on the resource-usage-dead-function test.

https://github.com/llvm/llvm-project/pull/77952