board: gateworks: venice: add imx8mm-gw7905-0x support

board: gateworks: venice: add imx8mm-gw7905-0x support

The Gateworks imx8mm-venice-gw7905-0x consists of a SOM + baseboard.

The GW700x SOM contains the following:
 - i.MX8M Mini SoC
 - LPDDR4 memory
 - eMMC Boot device
 - Gateworks System Controller (GSC) with integrated EEPROM, button
   controller, and ADC's
 - RGMII PHY
 - PMIC
 - SOM connector providing:
  - FEC GbE MII
  - 1x SPI
  - 2x I2C
  - 4x UART
  - 2x USB 2.0
  - 1x PCI
  - 1x SDIO (4-bit 3.3V)
  - 1x SDIO (4-bit 3.3V/1.8V)
  - GPIO

The GW7905 Baseboard contains the following:
 - GPS
 - microSD
 - off-board I/O connector with I2C, SPI, GPIO
 - EERPOM
 - PCIe clock generator
 - 1x full-length miniPCIe socket with PCI/USB3 (via mux) and USB2.0
 - 1x half-length miniPCIe socket with USB2.0 and USB3.0
 - USB 3.0 HUB
 - USB Type-C with USB PD Sink capability and peripheral support
 - USB Type-C with USB 3.0 host support

Signed-off-by: Tim Harvey <tharvey@gateworks.com>