Allow device to enter download mode on framework watchdog

This allows to get better insight of the device state at the
time of framework watchdog

Also, trigger sysRq after collecting traces

When system_server watchdog occurs, triggering sysRq can cause
watchdog bark and system_server traces is not generating. Trigger
sysRq after collecting traces

Change-Id: I504b66d2b63bf693d38eddb7d1f4122be307639a