ARM: STi: Add STiH418 SoC support

This patch adds support to STiH418 SoC.

Signed-off-by: Maxime Coquelin <[e-mail]>

Documentation/arm/sti/stih418-overview.txt

···
+			STiH418 Overview
+			================
+
+Introduction
+------------
+
+    The STiH418 is the new generation of SoC for UHDp60 set-top boxes
+    and server/connected client application for satellite, cable, terrestrial
+    and IP-STB markets.
+
+    Features
+    - ARM Cortex-A9 1.5 GHz quad core CPU (28nm)
+    - SATA2, USB 3.0, PCIe, Gbit Ethernet
+    - HEVC L5.1 Main 10
+    - VP9
+
+  Document Author
+  ---------------
+
+  Maxime Coquelin <[e-mail]>, (c) 2015 ST Microelectronics

Documentation/devicetree/bindings/arm/sti.txt

···
 Required root node property:
 compatible = "st,stih407";
 
+Boards with the ST STiH418 SoC shall have the following properties:
+Required root node property:
+compatible = "st,stih418";
+

arch/arm/mach-sti/board-dt.c

···
 	"st,stih415",
 	"st,stih416",
 	"st,stih407",
+	"st,stih418",
 	NULL
 };