uio: dfl: add vendor-specific feature id

uio: dfl: add vendor-specific feature id

Add a Device Feature List (DFL) feature id as a generic mechanism
to expose a vendor-specific FPGA IP to user space. The feature id
is intended for use with IPs that do not need any kernel services
beyond exposure to user space through the UIO DFL driver.

The feature id is used in, e.g., Intel Oak Springs Canyon IPUs
to expose various IPs to user space, e.g., Network Controller
Sideband Interface (NC-SI), BaseNIC, and VirtIO management.

Link: https://github.com/OPAE/dfl-feature-id
Signed-off-by: Peter Colberg <peter.colberg@intel.com>
Signed-off-by: Matthew Gerlach <matthew.gerlach@linux.intel.com>
Reviewed-by: Russ Weight <russell.h.weight@intel.com>
Link: https://lore.kernel.org/r/20230531030737.12989-1-peter.colberg@intel.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>