ath11k: add support for 6GHz radio in driver

This patch adds 6GHz band support and mac80211 registration for
the 6G phy radio.

Signed-off-by: Pradeep Kumar Chitrapu <pradeepc@codeaurora.org>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/20200603001724.12161-3-pradeepc@codeaurora.org