[AArch64][SVE] Asm: Support for insert element (INSR) instructions.

Insert general purpose register into shifted vector, e.g.
  insr    z0.s, w0
  insr    z0.d, x0

Insert SIMD&FP scalar register into shifted vector, e.g.
  insr    z0.b, b0
  insr    z0.h, h0
  insr    z0.s, s0
  insr    z0.d, d0

llvm-svn: 336979