Add KTR events for the PMAP interface functions

1. move unmapped_buf_allowed to machdep.c.
2. map both pmap_mapbios() and pmap_mapdev() to pmap_mapdev_attr() and have the actual work done by pmap_mapdev_priv() (renamed from pmap_mapdev()). Use pmap_mapdev_priv() to map the I/O port space because we can't use CTR() that early.
3. add pmap_pinit_common() that's used by both pmap_pinit0() and pmap_pinit(). Previously pmap_pinit0() would call pmap_pinit(), but that would create 2 KTR events. While here, use pmap_t instead of "struct pmap *".
4. fix pmap_kenter() to use vm_paddr_t as the type for the physical.
5. various white-space adjustments for consistency.
6. use C99 and KNF for function definitions where appropriate.
7. slightly re-order prototypes and defines in <machine/pmap.h>

No functional change (other than the creation of KTR_PMAP events).