Documentation: arm: update supported Marvell EBU processors

Now that we support Armada 37xx, let's add this family of SoC to the
Marvell documentation, and a reference to a link with more details about
those processors. As for Armda 39x, no datasheet is publicly
available at this time.
Signed-off-by: Gregory CLEMENT <gregory.clement@free-electrons.com>

Documentation/arm/Marvell/README

@@ -118,6 +118,19 @@ EBU Armada family
   Linux kernel mach directory: arch/arm/mach-mvebu
   Linux kernel plat directory: none
 
+EBU Armada family ARMv8
+-----------------------
+
+  Armada 3710/3720 Flavors:
+	88F3710
+	88F3720
+
+  Core: ARM Cortex A53 (ARMv8)
+
+  Homepage     : http://www.marvell.com/embedded-processors/armada-3700/
+
+  Device tree descritpion located in arch/arm64/boot/dts/marvell/armada-37*
+
 Avanta family
 -------------