AMDGPU: Prepare for reducing private element size.

Tests for the new scalarize all private access options will be
included with a future commit.

The only functional change is to make the split/scalarize behavior
for private access of > 4 element vectors to be consistent
with the flat/global handling. This makes the spilling worse
in the two changed tests.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@260804 91177308-0d34-0410-b5e6-96231b3b80d8
4 files changed