arm64, thunder: Add Kconfig option for Cavium Thunder SoC Family

This introduces ARCH_THUNDER to enable soc specific drivers and dtb
files.

Signed-off-by: Radha Mohan Chintakuntla <rchintakuntla@cavium.com>
Signed-off-by: Robert Richter <rrichter@cavium.com>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index fd4e81a..92f92fe 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -134,6 +134,11 @@
 
 menu "Platform selection"
 
+config ARCH_THUNDER
+	bool "Cavium Inc. Thunder SoC Family"
+	help
+	  This enables support for Cavium's Thunder Family of SoCs.
+
 config ARCH_VEXPRESS
 	bool "ARMv8 software model (Versatile Express)"
 	select ARCH_REQUIRE_GPIOLIB