Enforce -Wmissing-prototypes -Wstrict-prototypes for all ppc ports.
Split out macppc cpu support and make common to mpc6xx ports. Make
other mpc6xx ports use it. Add evcnts for mpc6xx traps.
"off_t" and the return value is a "paddr_t" to allow mappings
at offsets past 2^31 bytes. Somewhat inspired by FreeBSD, which
only changed the offset to a "vm_offset_t".
Includes updates for the i386, pc532 and sh3 mmmmap from Jason Thorpe.