ath9k: Enable TSF2 for generic HW timers

The base TSF is used for HW timers 0..7, but chips
in the AR9003 family and above can support more generic
timers. To use them, however, a second HW TSF needs to
be enabled. This patch allows usage of the extra
timers by starting the second TSF properly.

The extra set of HW timers is apparently also present
in AR9287, but we enable it only for the AR9003 family.

Cc: Kobi Cohen-Arazi <kobic@qti.qualcomm.com>
Signed-off-by: Sujith Manoharan <c_manoha@qca.qualcomm.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>