Largely eliminate the MD rwlock.h header file.

This was full of definitions that have been obsolete for over a
decade. The file still remains for __HAVE_RW_STUBS but that's all.
Used only internally in kern_rwlock.c now, not by <sys/rwlock.h>.

Major merge forward from matt-nb5-mips64.
New fixup code.
New common SPL code.
New common interrupt code.
Move related variables into structures.
Cleanup locore (move MD variable into it).
Kill StudlyCaps
Use PCU for FPU

branches: 1.7.22; 1.7.28; 1.7.30;
Remove clause 3 and 4 from TNF licenses

branches: 1.6.6; 1.6.8; 1.6.10;
Use new style memory barriers.

branches: 1.5.6;
RW_GIVE() needs to do a mb_memory() now.

- Change _lock_cas and friends to do "compare and swap" instead of "compare
and set".
- Rename them to _atomic_cas_uint, _atomic_cas_ulong etc and provide strong
aliases for the other names CAS goes by.

make kmutex_t and krwlock_t smaller by killing lock id.
ok'ed by Andrew Doran.

branches: 1.2.4; 1.2.8; 1.2.24; 1.2.26; 1.2.30; 1.2.32;
Merge newlock2 to head.

branches: 1.1.2;
file rwlock.h was initially added on branch newlock2.