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>
diff --git a/arch/arm64/configs/defconfig b/arch/arm64/configs/defconfig
index fbe250d..4c1a345 100644
--- a/arch/arm64/configs/defconfig
+++ b/arch/arm64/configs/defconfig
@@ -53,6 +53,7 @@
 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