arm64: dts: hisilicon: hi3660-hikey960: Allow USR4 LED to notify kernel panic

Blink the LED on a kernel panic.

Signed-off-by: Amit Kucheria <amit.kucheria@linaro.org>
Acked-by: Guodong Xu <guodong.xu@linaro.org>
Tested-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>