lantiq: vgv7510kw22: fix missing wireless

lantiq: vgv7510kw22: fix missing wireless

For some reason pin 7 (gphy0_led1_pins) need to be set to output prior
to loading the PCI driver. Otherwise the wireless doesn't appear on the
PCI bus. Of course, it doesn't make much sense, since pin 7 is used to
drive the LAN1 led.

It can either be done by setting the pins function to GPHY or GPIO +
direction output. However, the pinctrl driver doesn't provide a way to
switch a pin to GPIO. It is done indirectly by the pinctrl driver at the
time a GPIO is requested (requesting a GPIO always resets the function
to GPIO).

Do it via pinmux driver, as it is always loaded first. Use the GPHY
function as it's the pins intended purpose for this board.

Fixes: FS#2895
Signed-off-by: Mathias Kresin <dev@kresin.me>