[AMDGPU] Fix VOPD dependency checks during combine

[AMDGPU] Fix VOPD dependency checks during combine

Check superreg/subreg defs of an instruction when checking for
dependencies. This may cause some regressions, but better be
safe than sorry. Changed tests are affected because of the
implicit-defs of the superregs.

Differential Revision: https://reviews.llvm.org/D152943