cfg80211: add and expose HE 6 GHz band capabilities

cfg80211: add and expose HE 6 GHz band capabilities

These capabilities cover what would otherwise be transported
in HT/VHT capabilities, but only a subset thereof that is
actually needed on 6 GHz with HE already present. Expose the
capabilities to userspace, drivers are expected to set them
as using the 6 GHz band (currently) requires HE capability.

Link: https://lore.kernel.org/r/20200528213443.244cd5cb9db8.Icd8c773277a88c837e7e3af1d4d1013cc3b66543@changeid
Signed-off-by: Johannes Berg <johannes.berg@intel.com>