ath9k: General code scrub

Replace TRUE/FALSE macros with VALID/INVALID macros.
Follow a consistent variable convention.
Remove unnecessary comments.
Add all RC phy macros into a single enum.
Merge functions into reasonably sized entities.

Signed-off-by: Sujith <Sujith.Manoharan@atheros.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>