arm64: add ARCH_THUNDER2 to defconfig

This will allow the default kernel build to boot on Cavium ThunderX2
CN99XX processors.
Signed-off-by: Jayachandran C <jnair@caviumnetworks.com>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>

arch/arm64/configs/defconfig

@@ -53,6 +53,7 @@ CONFIG_ARCH_STRATIX10=y
 CONFIG_ARCH_TEGRA=y
 CONFIG_ARCH_SPRD=y
 CONFIG_ARCH_THUNDER=y
+CONFIG_ARCH_THUNDER2=y
 CONFIG_ARCH_UNIPHIER=y
 CONFIG_ARCH_VEXPRESS=y
 CONFIG_ARCH_VULCAN=y