drivers:
- Remove scsi_low_pisa.*, they were unused.
- Remove <compat/netbsd/physio_proc.h> and calls to the stubs in that
header. They were empty nops.
- Retire sl_xname and use device_get_nameunit() and device_printf() with
the underlying device_t instead.
- Remove unused {ct,ncv,nsp,stg}print() functions.
- Remove empty SOFT_INTR_REQUIRED() macro and the unused sl_irq member.