brcmfmac: announce P2P_DEVICE support in wiphy structure

P2P_DEVICE support was removed from brcmfmac for v3.9 kernel with
the commit below:

commit 1527c343
Author: Arend van Spriel <arend@broadcom.com>
Date:   Thu Apr 4 12:10:11 2013 +0200

    brcmfmac: remove advertising P2P device support

However, it got merged into wireless-next. But for 3.10 brcmfmac does
support P2P device. Putting it back with this commit.

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>