brcmfmac: add support for CQM RSSI notifications

Add support for CQM RSSI measurement reporting and advertise the
NL80211_EXT_FEATURE_CQM_RSSI_LIST feature. This enables a userspace
supplicant such as iwd to be notified of changes in the RSSI for roaming
and signal monitoring purposes.

Signed-off-by: Alvin Šipraga <alsi@bang-olufsen.dk>
Reviewed-by: Arend van Spriel <arend.vanspriel@broadcom.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/20210208125738.3546557-1-alsi@bang-olufsen.dk