brcmfmac: add peer-to-peer group discovery support

First part for P2P support. It is a variation on the existing
scanning functionality and is used to discover peer-to-peer
group owners and/or peer-to-peer devices in listen state.

Tested with wpa_cli/wpa_supplicant v2.0-devel.

Reviewed-by: Pieter-Paul Giesberts <pieterpg@broadcom.com>
Reviewed-by: Hante Meuleman <meuleman@broadcom.com>
Signed-off-by: Arend van Spriel <arend@broadcom.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>