pds_vdpa: Add new vDPA driver for AMD/Pensando DSC

This is the initial auxiliary driver framework for a new vDPA
device driver, an auxiliary_bus client of the pds_core driver.
The pds_core driver supplies the PCI services for the VF device
and for accessing the adminq in the PF device.

This patch adds the very basics of registering for the auxiliary
device and setting up debugfs entries.

Signed-off-by: Shannon Nelson <shannon.nelson@amd.com>
Acked-by: Jason Wang <jasowang@redhat.com>
Message-Id: <20230519215632.12343-4-shannon.nelson@amd.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>