kmsg_dump: add kmsg_dump() calls to the reboot, halt, poweroff and emergency_restart...

kmsg_dump: add kmsg_dump() calls to the reboot, halt, poweroff and emergency_restart paths

We need to know the reason why system rebooted in support service.
However, we can't inform our customers of the reason because final
messages are lost on current Linux kernel.

This patch improves the situation above because the final messages are
saved by adding kmsg_dump() to reboot, halt, poweroff and
emergency_restart path.

Signed-off-by: Seiji Aguchi <[email protected]>
Cc: David Woodhouse <[email protected]>
Cc: Marco Stornelli <[email protected]>
Reviewed-by: Artem Bityutskiy <[email protected]>
Reviewed-by: KOSAKI Motohiro <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>