[llvm] [GlobalISel] Build the split load value in an integer type in lowerLoad (PR #213694)

[Kacper Doga via llvm-commits]

varev-dev wrote:

Rebased on top of #214700 
Added float/pointer coverage
Reworded description to report generic legalization, not amdgpu selection gap

Now most of the diff is s32->i32 from pointer path

https://github.com/llvm/llvm-project/pull/213694