arm64: add mvebu architecture entry

The Armada 3700 is an mvebu ARM64 SoC using one or two Cortex-A53 cores
depending of the variant.
Signed-off-by: Gregory CLEMENT <gregory.clement@free-electrons.com>
Reviewed-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

arch/arm64/Kconfig.platforms

@@ -48,6 +48,12 @@ config ARCH_MEDIATEK
 	help
 	  Support for Mediatek MT65xx & MT81xx ARMv8 SoCs
 
+config ARCH_MVEBU
+	bool "Marvell EBU SoC Family"
+	help
+	  This enables support for Marvell EBU family such as the
+	  Armada 3700 SoC family.
+
 config ARCH_QCOM
 	bool "Qualcomm Platforms"
 	select PINCTRL