hostapd: add a build variant for wpa_supplicant with p2p (aka Wi-Fi Direct) support

Signed-off-by: Felix Fietkau <nbd@openwrt.org>

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@37739 3c298f89-4303-0410-b956-a3cf2f4a3e73