brcmfmac: support creation of P2P_DEVICE through user-space

The current driver code creates a P2P_DEVICE through a module
parameter. This device has a dummy netdevice which is not how this
interface type is intended. This patch add proper support for the
P2P_DEVICE interface type. This requires a wpa_supplicant with such
support as well.

Reviewed-by: Pieter-Paul Giesberts <pieterpg@broadcom.com>
Reviewed-by: Piotr Haber <phaber@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>