ARM: dts: imx6qdl-colibri: use pull-down on wake-up pin

The wake-up pin is pulled low with 100kOhm on the carrier board.
The current configuration of 100kOhm pull-up caused lots of
interrupts, especially during boot up. Make sure the pin is at a
reasonable level at startup by pulling it low on SoC side too.

Signed-off-by: Stefan Agner <stefan@agner.ch>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>