ath9k: Enable manual peak detect calibration

On some AR955x/QCA953x boards, noise floor calibration
gets stuck and the cause is a hardware/BB issue. To fix
this, peak detect calibration in the HW is disabled
and is done in the driver instead. There a few differences
with the calibration routine for older chips like
AR9331.

Signed-off-by: Sujith Manoharan <c_manoha@qca.qualcomm.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>