o) Use inline functions to access coprocessor 0 registers rather than external

o) Use inline functions to access coprocessor 0 registers rather than external
   ones implemented using assembly.
o) Use TRAPF_USERMODE() consistently rather than USERMODE().  Eliminate
   <machine/psl.h> as a result.
o) Use intr_*() rather than *intr(), consistently.
o) Use register_t instead of u_int in some trap code.
o) Merge some more endian-related macros to machine/asm.h from NetBSD.
o) Add PTR_LI macro, which loads an address with the correct sign-extension for
   a pointer.
o) Restore interrupts when bailing out due to an excessive IRQ in
   nexus_setup_intr().
o) Remove unused functions from psraccess.S.
o) Enter temporary virtual entries for large memory access into the page tables
   rather than simply hoping they stay resident in the TLB and we don't need to
   do a refill for them.
o) Abstract out large memory mapping setup/teardown using some macros.
o) Do mips_dcache_wbinv_range() when using temporary virtual addresses just
   like we do when we can use the direct map.