ARM: dts: imx6qdl-apalis: Add sleep state to can interfaces

This patch prepares the devicetree for the new Ixora V1.2 where we are
able to turn off the supply of the can transceiver. This implies to use
a sleep state on transmission pins in order to prevent backfeeding.

Signed-off-by: Philippe Schenker <philippe.schenker@toradex.com>
Acked-by: Marcel Ziswiler <marcel.ziswiler@toradex.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>