radeonsi: Remove use.sgpr* intrinsics, use load instructions instead

radeonsi: Remove use.sgpr* intrinsics, use load instructions instead

We now model loading uses sgpr values with LLVM IR load instructions that
use the USER_SGPR address space.

The definition of the sgpr parameter to the use_sgpr() helper function
in radeonsi_shader.c has changed so that you can pass raw sgpr values
rather than having to divide the sgpr value you want to use by the dword
width of the type you want to load.