ARM: kirkwood: ioremap the cpu_config register before using it.

With the move to mach-mvebu and MULTI_V5, the global iomap for all
registers will be going away. So explicitly map the CPU configuration
register before using it.

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>