arm64: defconfig: enable new trigger modes for leds

Most development boards and devices have one or more LEDs. It is useful
during debugging if they can be wired to show different behaviours such as
disk or cpu activity or a load-average dependent heartbeat. Enable panic
and disk activity triggers so they can be tied to LED activity during
debugging as well.

Signed-off-by: Amit Kucheria <amit.kucheria@linaro.org>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>