ath9k_hw: clean up calibration flags

The calibration actual calibration flags are only used by the per chip family
source files, so it makes more sense to define them in those files instead
of globally. That way the code has to test for less flags.

Also instead of using a separate callback for testing whether a particular
calibration type is supported, simply adjust ah->supp_cals in the calibration
init which is called right after the hardware reset, before any of the
calibrations are run.

Signed-off-by: Felix Fietkau <nbd@openwrt.org>
Signed-off-by: John W. Linville <linville@tuxdriver.com>