ath9k_hw: move TX/RX gain INI stuff to its own hardware family code

The AR9003 TX/RX gain is currently initialized with the other
components, so for now AR9003 does not implment this callback,
after hardware bring up  we can test moving the TX/RX gain there
as well and if it works well move them to its own callback as
well.

Since all INI stuff is now moved out hw.c no longer needs to
include and touch any original INI headers/structs.

Signed-off-by: Luis R. Rodriguez <lrodriguez@atheros.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>