[AArch64][SVE] Add SVE intrinsic for LD1RQ

Summary:
Adds the following intrinsic for contiguous load & replicate:
  - @llvm.aarch64.sve.ld1rq

The LD1RQ intrinsic only needs the SImmS16XForm added by this
patch. The others (SImmS2XForm, SImmS3XForm & SImmS4XForm)
were added for consistency.

Reviewers: andwar, sdesmalen, efriedma, cameron.mcinally, dancgr, rengolin

Reviewed By: sdesmalen

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

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D76929