cfg80211: add 6GHz UNII band definitions

For the new 6GHz there are new UNII band definitions as listed
in the FCC notice [1].

[1] https://docs.fcc.gov/public/attachments/FCC-18-147A1_Rcd.pdf

Reviewed-by: Pieter-Paul Giesberts <pieter-paul.giesberts@broadcom.com>
Reviewed-by: Leon Zegers <leon.zegers@broadcom.com>
Signed-off-by: Arend van Spriel <arend.vanspriel@broadcom.com>
Link: https://lore.kernel.org/r/1564745465-21234-3-git-send-email-arend.vanspriel@broadcom.com
Signed-off-by: Johannes Berg <johannes.berg@intel.com>