ARM: dts: armada-385-synology-ds116: add support for Synology DS116 NAS

This commit adds the device tree description for the Synology DS116 NAS.

It is a one-bay NAS powered by a Marvell Armada 385 at 1.866 GHz. The
device features the following items :
  - 1 GB DDR3 RAM
  - a 8MB SPI flash
  - 2 USB3 ports, power-controlled via a GPIO for each
  - 1 gigabit ethernet interface connected over SGMII to a 88e1514 phy
  - a single SATA port, power-controlled via a GPIO
  - a battery-powered RTC
  - one UART connected to the serial console (2mm connector on board)
  - the Tx line of the second UART connected to a PIC microcontroller
    dealing with beep, reset, power-off and LED blinking (9600 Bps)
  - some of the front-panel LEDs are connected to GPIOs, one is directly
    connected to the SATA link to report disk activity.
  - a GPIO-controlled fan (3 bits for 7 speeds and OFF)

With this DTS, my NAS is 100% functional starting with kernel 4.9.

Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: Willy Tarreau <w@1wt.eu>
Signed-off-by: Gregory CLEMENT <gregory.clement@free-electrons.com>