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

[Austin Kerbow via llvm-commits]

kerbowa wrote:

> > 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
> 
> @arsenm Is there any documentation about the hardware and ABI besides the SDAG implementation?

https://llvm.org/docs/AMDGPUUsage.html#preloaded-kernel-arguments

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