plat: marvell: Add support for Armada-37xx SoC platform

Add supprot for Marvell platforms based on Armada-37xx SoC.
This includes support for the official Armada-3720 modular
development board and EspressoBin community board.
The Armada-37xx SoC contains dual Cortex-A53 Application CPU,
single secure CPU (Cortex-M3) and the following interfaces:
- SATA 3.0
- USB 3.0 and USB 2.0
- PCIe
- SDIO (supports boot from eMMC)
- SPI
- UART
- I2c
- Gigabit Ethernet

Signed-off-by: Konstantin Porotchkin <kostap@marvell.com>