reboot: arm: prepare reboot_mode for moving to generic kernel code

Prepare for the moving the parsing of reboot= to the generic kernel code
by making reboot_mode into a more generic form.

Change-Id: I5e4968c54b14e1ccef1e390975d99c2a5a57b00c
Signed-off-by: Robin Holt <holt@sgi.com>
Cc: Russell King <rmk+kernel@arm.linux.org.uk>
Cc: Russ Anderson <rja@sgi.com>
Cc: Robin Holt <holt@sgi.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Guan Xuetao <gxt@mprc.pku.edu.cn>
Acked-by: Russell King <rmk+kernel@arm.linux.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Git-commit: 16d6d5b00ee75307bab7e4ede9452c97b28f30e2
Git-Repo: git://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/


Signed-off-by: Abhimanyu Kapur <abhimany@codeaurora.org>