Verified that the NVRAM device (if supported) is still discovered, and
that NVRAM lookups succeed, e.g.:
bwn0: got macaddr 68:a3:c4:25:fa:5a
Tested on:
- BCM4312 (siba, bhndb-attached nvram)
- BCM43225 (bcma, chipc-attached nvram)
- RT-N53 (mips/bcma, nvram support unimplemented)