ARM: dts: imx6q-dhcom: Enable CAN in board DTS

Move the CAN enablement from SoM DTSi to board DTS, as each board might need
different CAN configuration. Moreover, disable CAN2 on the PDK2 as it is not
available on any connector. This also fixes on-SoM SD slot operation, as it
shares pins with the CAN2.

Signed-off-by: Marek Vasut <marex@denx.de>
Reviewed-by: Fabio Estevam <festevam@gmail.com>
Cc: Fabio Estevam <festevam@gmail.com>
Cc: Ludwig Zenz <lzenz@dh-electronics.com>
Cc: Shawn Guo <shawnguo@kernel.org>
Cc: NXP Linux Team <linux-imx@nxp.com>
To: linux-arm-kernel@lists.infradead.org
Signed-off-by: Shawn Guo <shawnguo@kernel.org>