arm64, defconfig: Enable Cavium Thunder SoC in defconfig

This patch enables Thunder SoCs in the arm64 defconfig. This is
esp. useful to add Thunder platforms to automated builds based on
arm64 defconfig.

Signed-off-by: Robert Richter <rrichter@cavium.com>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>

arch/arm64/configs/defconfig

@@ -32,6 +32,7 @@ CONFIG_MODULES=y
 CONFIG_MODULE_UNLOAD=y
 # CONFIG_BLK_DEV_BSG is not set
 # CONFIG_IOSCHED_DEADLINE is not set
+CONFIG_ARCH_THUNDER=y
 CONFIG_ARCH_VEXPRESS=y
 CONFIG_ARCH_XGENE=y
 CONFIG_SMP=y