[AMDGPU] Optimze old value of v_mov_b32_dpp

We can eliminate old value if bound_ctrl = 1 and row_mask = bank_mask = 0xf.
This is alternative implementation working with the intrinsic in InstCombine.
Original review for past-ISel optimization: D46570.

Differential Revision: https://reviews.llvm.org/D46596

llvm-svn: 332956