ARM: dts: imx6qdl-gw54xx: add CAN regulator

The GW54xx has a transceiver with a STBY pin connected to an IMX6 GPIO.
Configure this as a regulator to drive it low when CAN is in use.

Signed-off-by: Tim Harvey <tharvey@gateworks.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>