[ARM] 3593/1: Add reboot and shutdown handlers for Zaurus handhelds

Patch from Richard Purdie

Add functionality to allow machine specific reboot handlers on ARM.
Add machine specific reboot and poweroff handlers for all PXA Zaurus
models.

Signed-off-by: Richard Purdie <rpurdie@rpsys.net>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>