[llvm] [AMDGPU][GlobalISel] Enable kernel argument preloading (PR #134655)

[Matt Arsenault via llvm-commits]

arsenm wrote:

> @arsenm do we want to skip kern arg preloading if the argument is not used? This kind of makes the tests in their current form a bit pointless.

I'm pretty sure you you need to preload a consecutive block, so you need to preload unused arguments if it is in the middle of other useful arguments to preload 

https://github.com/llvm/llvm-project/pull/134655