[AArch64] Add instruction selection for strict FP

This consists of marking the various strict opcodes as legal, and
adjusting instruction selection patterns so that 'op' is 'any_op'.

FP16 and vector instructions additionally require some extra work in
lowering and legalization, so we can't set IsStrictFPEnabled just yet.
Also more work needs to be done for full strict fp support (marking
instructions that can raise exceptions as such, and modelling FPCR use
for controlling rounding).

Differential Revision: https://reviews.llvm.org/D114946