ath6kl: Add wow multicast firmware capability support

Infrastructure to enable Multicast WOW support based on
firmware capability added to the driver.This enables
different customers or chips to control this feature based
on firmware capability.

kvalo: Firmware capability infrastructure for multicast wow feature,
indetation fixes.

Signed-off-by: Naveen Gangadharan <ngangadh@qca.qualcomm.com>
Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>