mwifiex: Start P2P devices in P2P mode

p2p devices should identify themselves as such to userspace at
startup, so the connection manager can decide which interface
to start wpa_supplicant instances on.

Signed-off-by: Paul Stewart <pstew@chromium.org>
Reviewed-by: Bing Zhao <bzhao@marvell.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>