ath6kl: support fw reporting phy capabilities

Currently the supported bands are just hard coded in the driver.
However, the ath6kl FW will include its 11n and band capabilites in a
WMI_READY event. Handle this and report capabilites to cfg80211
accordingly.

Signed-off-by: Thomas Pedersen <c_tpeder@qca.qualcomm.com>
Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>