[AArch64] Add lowering pattern for scalar fp16 facge and facgt

Summary: The fp16 scalar version of facge and facgt requires a custom patter matching, as the result type is not the same width of the operands.

Reviewers: olista01, javed.absar, pbarrio

Reviewed By: javed.absar

Subscribers: kristof.beyls, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D60212

llvm-svn: 358083