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