cfg80211: adapt to new channelization of the 6GHz band

cfg80211: adapt to new channelization of the 6GHz band

The 6GHz band does not have regulatory approval yet, but things are
moving forward. However, that has led to a change in the channelization
of the 6GHz band which has been accepted in the 11ax specification. It
also fixes a missing MHZ_TO_KHZ() macro for 6GHz channels while at it.

This change is primarily thrown in to discuss how to deal with it.
I noticed ath11k adding 6G support with old channelization and ditto
for iw. It probably involves changes in hostapd as well.

Cc: Pradeep Kumar Chitrapu <pradeepc@codeaurora.org>
Cc: Jouni Malinen <jouni@w1.fi>
Signed-off-by: Arend van Spriel <arend.vanspriel@broadcom.com>
Link: https://lore.kernel.org/r/edf07cdd-ad15-4012-3afd-d8b961a80b69@broadcom.com
Signed-off-by: Johannes Berg <johannes.berg@intel.com>