[llvm] [AMDGPU] Update base addr of dyn alloca considering GrowingUp stack (PR #119822)

[via llvm-commits]

easyonaadit wrote:

> @s-barannikov hi, do you feel some more changes are required or may I go ahead and merge this?

I am merging it for now, let me know if any additional changes are required. 

https://github.com/llvm/llvm-project/pull/119822