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

[brooks]

Summary

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

Test Plan

a mips64 system boots, more testing appareciated

[kib]

sys/mips/mips/support.S

297

I suggest to move the store out of the pcb_onfault protected region.

[brooks]

• Move the store of value out of the pcb_onfault protected region.
• Finish updating a comment.