qtnfmac: implement extendable channel survey dump

Switch to extendable implementation of channel survey dump to make sure
that any new channel statistics can be added in the future without any
backwards compatibility issues. For this purpose use a separate variable
length bitmap to pass the list of valid statistics in firmware response.
Besides, switch to using channel frequency instead of IEEE channel
number to prepare for adding support of 6GHz band.

Signed-off-by: Igor Mitsyanko <igor.mitsyanko.os@quantenna.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>