[AArch64][SVE] Asm: Support for contiguous, first-faulting LDFF1 (scalar+scalar) load instructions.

Reviewers: fhahn, rengolin, samparker, SjoerdMeijer, t.p.northover, echristo, evandro, javed.absar

Reviewed By: rengolin

Subscribers: tschuett, kristof.beyls, llvm-commits

Differential Revision: https://reviews.llvm.org/D45946

llvm-svn: 330697