boards: meson: add g12a u200

The Amlogic U200 board is based on the Amlogic S905D2 SoC
from the Amlogic G12A SoC family.

The board has the following specifications :
 - Amlogic S905D2 ARM Cortex-A53 quad-core SoC
 - XGB DDR4 SDRAM
 - 10/100 Ethernet (Internal PHY)
 - 1 x USB 3.0 Host
 - eMMC
 - SDcard
 - Infrared receiver
 - SDIO WiFi Module
 - MIPI DSI Connector
 - Audio HAT Connector
 - PCI-E M.2 Connector

Signed-off-by: Jerome Brunet <jbrunet@baylibre.com>
Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>