[ARM] S3C64XX: Add generic s3c64xx sys device.

Add an s3c64xx_sysclass and device for items that currently
want to bind to any s3c64xx processor. The first user of this
will be parts of the s3c64xx suspend support which need to
save device state over suspend/resume.

Signed-off-by: Ben Dooks <ben-linux@fluff.org>