[AArch64][SVE] Add wide compare immediate patterns

Summary:
Recognize wide compares where the wide operand is a splat of a scalar
value in the appropriate range and convert to the immediate variant of
the instruction.

Patch by Graham Hunter

Reviewers: sdesmalen, efriedma, dancgr, rovka, rengolin

Reviewed By: efriedma

Subscribers: tschuett, kristof.beyls, hiraditya, rkruppe, psnobl,
llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D71009