pds_core: add initial VF device handling

This is the initial VF PCI driver framework for the new
pds_vdpa VF device, which will work in conjunction with an
auxiliary_bus client of the pds_core driver.  This does the
very basics of registering for the new VF device, setting
up debugfs entries, and registering with devlink.

Signed-off-by: Shannon Nelson <shannon.nelson@amd.com>
Acked-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>