[AArch64][SVE] Asm: Support for vector element FP compare.

Contains the following variants:

- Compare with (elements from) other vector
  instructions: fcmeq, fcmgt, fcmge, fcmne, fcmuo.
  aliases: fcmle, fcmlt.

  e.g. fcmle   p0.h, p0/z, z0.h, z1.h => fcmge p0.h, p0/z, z1.h, z0.h

- Compare absolute values with (absolute values from) other vector.
  instructions: facge, facgt.
  aliases: facle, faclt.

  e.g. facle   p0.h, p0/z, z0.h, z1.h => facge   p0.h, p0/z, z1.h, z0.h

- Compare vector elements with #0.0
  instructions: fcmeq, fcmgt, fcmge, fcmle, fcmlt, fcmne.

  e.g. fcmle   p0.h, p0/z, z0.h, #0.0

llvm-svn: 336182