ARM: dts: imx6q: Add Variscite MX6 Custom board support

ARM: dts: imx6q: Add Variscite MX6 Custom board support

This patch adds support for the Variscite MX6 SoM Carrier Board.

This Carrier-Board has the following :
- LVDS interface for the VLCD-CAP-GLD-LVDS 7" LCD 800 x 480 touch display
- HDMI Connector
- USB Host + USB OTG Connector
- 10/100/1000 Mbps Ethernet
- miniPCI-Express slot
- SD Card connector
- Audio Headphone/Line In jack connectors
- S-ATA
- On-board DMIC
- RS485 Header
- CAN bus header
- SPI header
- Camera Interfaces header
- OnBoard RTC with Coin Backup battery socket
- RS232 Debug Header (IDC10)
- RS232 DTE

Product Page : https://www.variscite.com/product/single-board-computers/var-mx6customboard

The dts file based on the ones provided by Variscite on their own
kernel, but adapted for mainline.

Cc: Pierluigi Passaro <pierluigi.p@variscite.com>
Reviewed-by: Fabio Estevam <festevam@gmail.com>
Signed-off-by: Gregory CLEMENT <gregory.clement@bootlin.com>
Signed-off-by: James Hilliard <james.hilliard1@gmail.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>