[ARM,MVE] Add intrinsics for abs, neg and not operations.

[ARM,MVE] Add intrinsics for abs, neg and not operations.

Summary:
This commit adds the unpredicated intrinsics for the unary operations
vabsq (absolute value), vnegq (arithmetic negation), vmvnq (bitwise
complement), vqabsq and vqnegq (saturating versions of abs and neg for
signed integers, in the sense that they give INT_MAX if an input lane
is INT_MIN).

This is done entirely in clang: all of these operations have existing
isel patterns and existing tests for them on the LLVM side, so I've
just made clang emit the same IR that those patterns already match.

Reviewers: dmgreen, miyuki, MarkMurrayARM, ostannard

Reviewed By: MarkMurrayARM

Subscribers: kristof.beyls, cfe-commits

Tags: #clang

Differential Revision: https://reviews.llvm.org/D74331