pds_core: devlink params for enabling VIF support

Add the devlink parameter switches so the user can enable
the features supported by the VFs.  The only feature supported
at the moment is vDPA.

Example:
    devlink dev param set pci/0000:2b:00.0 \
	    name enable_vnet cmode runtime value true

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>