UPSTREAM: GKI: 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.

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>
(cherry picked from commit b287a25a7148a89d977c819c1f7d6584f875b682)
Signed-off-by: Mark Salyzyn <salyzyn@google.com>
Bug: 154175554
Change-Id: Id1075f4d97eddb818aa495903a7643958e6c73d6