board: gateworks: venice: add imx8mp-venice-gw740x support

board: gateworks: venice: add imx8mp-venice-gw740x support

The GW74xx is based on the i.MX 8M Plus SoC featuring:
 - LPDDR4 DRAM
 - eMMC FLASH
 - Gateworks System Controller
 - PCIe Gen 3.0 switch (build option)
 - USB 3.0 HUB
 - USB Type-C front panel connector
 - GPS
 - 3-axis accelerometer
 - CAN bus
 - 6x GbE RJ45 front-panel jacks
  - 1x IMX8M FEC RGMII GbE (with Passive PoE)
  - 5x IMX8M EQOS RGMII 6 port GbE Switch
    (1x with 802.3af class 5 Active PoE)
 - RS232/RS485/RS422 serial transceiver
 - MIPI header (DSI/CSI/GPIO/PWM/I2S)
 - DigI/O header (UART/GPIO/I2C/ADC)
 - 802.11ac WiFi
 - Bluetooth BLE
 - 3x MiniPCIe sockets with PCI/USB
 - 1x M.2 Socket with USB2.0, PCIe, and dual-SIM
 - PMIC
 - Wide range DC input supply (8V to 60V DC)

Do the following to add support for this and future imx8mp-venice boards:
 - add dts
 - add DRAM config
 - add PMIC config
 - add IMX8MP support in spl.c and venice.c

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