[SVE] Fix shift-by-imm patterns used by asr, lsl & lsr intrinsics.

Right shift patterns will no longer incorrectly accept a shift
amount of zero.  At the same time they will allow larger shift
amounts that are now saturated to their upper bound.

Patterns have been extended to enable immediate forms for shifts
taking an arbitrary predicate.

This patch also unifies the code path for immediate parsing so the
i64 based shifts are no longer treated specially.

Differential Revision: https://reviews.llvm.org/D86084