ath9k: move driver core helpers to main.c

Keep on btcoex.c only hardware access helpers, move the
driver core specific code to main.c. To accomplish
this we had to split ath_init_btcoex_info() into two parts,
the driver core part -- ath_init_btcoex_timer() and the hw
specific part -- ath9k_hw_init_btcoex_hw_info(). This
highlights how ath_gen_timer is part of the driver core, not
hw related, so stuff that into ath_btcoex struct.

The ath9k_hw_btcoex_init() code is now put inline on
ath_init_softc() through a switch to it easier to follow,
since we did that we can now call ath_tx_get_qnum() from
the main.c instead of btcoex.c

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