Update the pmax SCSI drivers (rz and tz) to use <machine/conf.h>.
Fix the driver entry points to have the correct signatures -- add
"ioflag" args to read() and write(), add "struct proc *p" arg to
open and close.
Stop using __BDEVSW_DUMP_OLD_TYPE, and update the rzdump and tzdump
entry points to have the correct, MI signatures.
NB: this is just syntactic sugar: both the caller and the dump entry
points ignore the additional args, and do exactly what they did before.
This must be fixed before using dump entry points in non-pmax drivers
(e.g., the MI scsi code).