[AMDGPU] Track liveins for max-ilp-sched-strategy

Even if optimizing for ILP, it is still useful to track RP to avoid spilling. Given that, we need to maintin consistent liveness state with the RP tracker. This patch makes RP tracking consistent by updating for liveins.

Otherwise, we should completely eliminate RP tracking for this scheduler (checkScheduling, initCandidate).

Differential Revision: https://reviews.llvm.org/D149358