Sysace: Move structure allocation from bus binding into common code

Split the determination of device registers/irqs/etc from the actual
allocation and initialization of the device structure.  This cleans
up the code a bit in preparation to add an of_platform bus binding

Signed-off-by: Grant Likely <grant.likely@secretlab.ca>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>