ARM: dts: mvebu: add device tree for netgear gs110emx switch

Add the device tree for a Netgear GS110EMX switch featuring 8 Gigabit
ports and 2 Multi-Gig ports (100M/1G/2.5G/5G/10G). An 88E6390X switch
sits at its core connecting to two 88X3310P 10G PHYs. The control plane
is handled by an 88F6811 Armada 381 SoC.

The following functionality is tested:
- 8 gigabit Ethernet ports connecting via 88E6390X to the 88F6811
- serial console UART
- 128 MB commercial grade DDR3L SDRAM
- 16 MB serial SPI NOR flash

The two 88X3310P 10G PHYs while detected during boot seem neither to
detect any link nor pass any traffic.

Signed-off-by: Marcel Ziswiler <marcel@ziswiler.com>
Signed-off-by: Gregory CLEMENT <gregory.clement@bootlin.com>