Many systems (e.g. embedded systems) do not have wifi modules connected to
bluetooth modules, so bluetooth coexistence is irrelevant there. With the
addition of MCI support, ath9k picked up quite a bit of extra code that
can be compiled out this way.

This patch redefines ATH9K_HW_CAP_MCI and adds an inline wrapper for
querying the bluetooth coexistence scheme, allowing the compiler to
eliminate code that uses it, with only very little use of #ifdef.

On MIPS this reduces the total size for the modules by about 20k.

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