[AArch64][SVE] Asm: Add support for (mov|dup) of scalar

Summary: This patch adds support for 'dup' (Scalar -> SVE) and its corresponding 'mov' alias.

Reviewers: fhahn, rengolin, evandro, echristo

Reviewed By: fhahn

Subscribers: aemerson, javed.absar, tschuett, kristof.beyls, llvm-commits

Differential Revision: https://reviews.llvm.org/D41822

llvm-svn: 322172