The current Rockchip platform code retains the "common" default panic
handler which simply hangs the system (until the watchdog kicks in, if
enabled). This is usually not a great user experience.

This patch implements a Rockchip-specific panic handler that calls the
platform's reboot implementation to reset the system.

Change-Id: I4cbe09c48f1b3f86ebdfc0108c186565f9ffc119
Signed-off-by: Julius Werner <jwerner@chromium.org>