[AMDGPU] Resolve pseudo registers at encoding uses

Pseudo-registers allow different register encodings
between gpu generations. Make sure we resolve the
pseudo regs to real regs whenever we get their
hardware encoding.
Using the correct encodings revealed a register
bank conflict and an unnecessary write dependency.
Tests have been updated to match.

Reviewed By: rampitec

Differential Revision: https://reviews.llvm.org/D90721

Change-Id: I73c154cd24aecc820993b50bebaf4df97a5710ca