Add full softfloat and hardfloat support for MIPS.
This adds new target architectures for hardfloat:
mipselhf mipshf mips64elhf mips64hf.
Tested in QEMU only.
Sponsored by: DARPA, AFRL
Sponsored by: HEIF5
Differential Revision: https://reviews.freebsd.org/D8376