ARM: mvebu: add support for the new Armada 385 based Linksys boards

This patch adds support for the Linksys WRT1200AC (Caiman) and
the Linksys WRT1900AC v2 (Cobra).

Both boards have:

- 2 Marvell 88W8864 radios
- 1 USB 3.0 port
- 1 USB 2.0/eSATAp port
- 2 Ethernet interfaces connected to a 88E6176 switch (1x WAN + 4x LAN)
- 128MB NAND flash
- 512MB RAM

gregory.clement@free-electrons.com: use serial0:115200n8 in
stdout-path and remove the bootargs part in the chosen node

Signed-off-by: Imre Kaloz <kaloz@openwrt.org>
Acked-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: Gregory CLEMENT <gregory.clement@free-electrons.com>