AMDGPU: Correct const_index_stride for wave 32 for PAL ABI

Retrying after revert and fix (removed implicit def flag from operand). Now
passes with expensive_checks enabled.

Since there is a single scratch resource descriptor for all shaders, if there is
a wave32 and a wave64 shader (for instance for VsFs pairs)
then the const_index_stride will be incorrect for wave32 shaders.

Differential Revision: https://reviews.llvm.org/D101830

Change-Id: Ie3b8b2921237968caca91527dd0c97b1b0cc0360