ARM: mvebu: Let kirkwood use the system controller for restart

The mvebu system controller already supports restarting orion
systems. Remove all the C code which will be replaced by the system
controller.

Signed-off-by: Andrew Lunn <andrew@lunn.ch>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Tested-by: Jason Gunthorpe <jgunthorpe@obsidianresearch.com>
Signed-off-by: Jason Cooper <jason@lakedaemon.net>