microblaze: Modify pci specific code to support multidomain

microblaze: Modify pci specific code to support multidomain

Proc entries will be created for every pci bus.
With current implementation,in multidomain same bus number
will repaeat but in different domain, which causes kernel crash
as already same bus number exists.

Return domain number when kernel requests while creating proc
entries for each bus.

Signed-off-by: Bharat Kumar Gogada <bharatku@xilinx.com>
Signed-off-by: Michal Simek <michal.simek@xilinx.com>