power: reset: Add qcom reboot reason driver

Add support for setting reboot reason on Qualcomm boards. This driver
uses reboot notifier chain to support commands such as "reboot
bootloader" to boot board to fastboot mode.

Change-Id: I3ccaa926dc92df9d0acd4261c79ff7f3c9e1c438
Signed-off-by: Elliot Berman <eberman@codeaurora.org>