ath5k: use regulatory infrastructure

Make ath5k select the ath module and add in the hooks to make the
eeprom regulatory hint and reg notifier take effect.

Changes to attach.c
Changes-licensed-under: ISC

Changes to base.c
Changes-licensed-under: 3-Clause-BSD

Signed-off-by: Bob Copeland <me@bobcopeland.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>