ARM: dts: imx6q-dhcom: Add DH 560-200 display unit support

Add DT bits to support the DH 560-200 display unit, which can be plugged
into the side of the PDK2 board. The display unit contains a display, EDT
ETM0700G0EDH6 and an EDT FT5x06 touchscreen controller.

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