pinctrl: dt-bindings: Fix the armada-37xx documentation

While it was possible to configure the PCIe1 Wakeup pin, it was missing
in the bidding, let's document it.

Signed-off-by: Gregory CLEMENT <gregory.clement@bootlin.com>
Tested-by: Miquel Raynal <miquel.raynal@bootlin.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>