MIPS: Implement fue*word* and casueword* in assembly.

Remove NO_FUEWORD so the 'e' variants are wrapped by the non-'e'
variants. This is more correct and leaves sparc64 as the outlier.

Reviewed by: jmallett, kib
Obtained from: CheriBSD
Sponsored by: DARPA, AFRL
Differential Revision: https://reviews.freebsd.org/D14603