imx7d-pico has an ap6212 wifi chip connected to usdhc2 port.

Add support for the usdhc2 port and to the WL_REG_ON regulator
so Wifi can be functional on this board.
Signed-off-by: Vanessa Maegima <vanessa.maegima@nxp.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>