[AArch64][SVE] Add first-faulting load intrinsic

Summary:
Implements the llvm.aarch64.sve.ldff1 intrinsic and DAG
combine rules for first-faulting loads with sign & zero extends

Reviewers: sdesmalen, efriedma, andwar, dancgr, rengolin

Reviewed By: sdesmalen

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

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D73025