panic/reboot: allow specifying reboot_mode for panic only

Allow specifying reboot_mode for panic only.  This is needed on systems
where ramoops is used to store panic logs, and user wants to use warm
reset to preserve those, while still having cold reset on normal
reboots.

Change-Id: Id1075f4d97eddb818aa495903a7643958e6c73d6
Link: http://lkml.kernel.org/r/20190322004735.27702-1-aaro.koskinen@iki.fi


Signed-off-by: Aaro Koskinen <aaro.koskinen@nokia.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Git-commit: b287a25a
Git-repo: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git


Signed-off-by: Prasad Sodagudi <psodagud@codeaurora.org>