ARM: dts: imx7d-sdb: Add Wifi support

imx7d-sdb has a BCM4339 Wifi chip connected to USDHC2.

Add support for it.

While at it, move the WL_REG_ON pin to the correct pinctrl node.

Signed-off-by: Fabio Estevam <fabio.estevam@nxp.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>