- convert PRVERB to use device_printf()

- convert PRVERB to use device_printf()
- add aha_softc.dev
- push "dev" into aha_alloc() instead of "unit" in order to convert printf() to
  device_printf() in aha_alloc().  change aha_alloc() declaration in ahareg.h
  accordingly
- printf("aha%d str", aha->unit) ==> device_printf(aha->dev, "str")
- in aha_alloc(), aha_free() and aha_attach(), use device_get_unit(aha->dev)
  to get the device unit instead of using aha->unit directly
- remove aha_softc.unit

Submitted-by: Sarunas Vancevicius <svan at redbrick.dcu.ie>