ARM: mvebu: Add Device Tree description of the Armada 388 SoC

This SoC belongs to the Armada 38x family. The main difference with
the Armada 385 is that the 388 can handle two more SATA
ports. Currently the consequence is the use of a different compatible
string for the pinctrl node, in order to be able to use the pins
associated to this 2 new SATA ports. The second SATA controller has
also been moved from the armada38x.dtsi as it it specific to the
Armada388 version.

In the same time the Armada385 DB and Armada 385 RD board have been
renamed in the 388 one and now include the armada-388.dtsi file. AS
both of them have 4 SATA ports the SoC used on them were wrongly
described.

Signed-off-by: Gregory CLEMENT <gregory.clement@free-electrons.com>
Signed-off-by: Andrew Lunn <andrew@lunn.ch>