[AArch64][SVE] Asm: Support for predicated FP operations.

This patch adds support for the following floating point
instructions:
  FABD   (absolute difference)
  FADD   (addition)
  FSUB   (subtract)
  FSUBR  (subtract reverse form)
  FDIV   (divide)
  FDIVR  (divide reverse form)
  FMAX   (maximum)
  FMAXNM (maximum number)
  FMIN   (minimum)
  FMINNM (minimum number)
  FSCALE (adjust exponent)
  FMULX  (multiply extended)

All operations are predicated and binary form, e.g.

  fadd z0.h, p0/m, z0.h, z1.h
        ^___________^ (tied)

Supporting 16, 32 and 64-bit FP elements.

llvm-svn: 337259