[Loop Peeling] Separate the Loop Peeling Utilities from the Loop Unrolling Utilities

Summary: This patch separates the Loop Peeling Utilities from Loop Unrolling.
The reason for this change is that Loop Peeling is no longer only being used by
loop unrolling; Patch D82927 introduces loop peeling with fusion, such that
loops can be modified to have to same trip count, making them legal to be
peeled.

Reviewed By: Meinersbur

Differential Revision: https://reviews.llvm.org/D83056