Add callback that is called by epautoconf to allow UDC driver match the
best endpoint for specific descriptor. It's intended to supply mechanism
which allows to get rid of chip-specific endpoint matching code from
epautoconf.

If gadget has set 'ep_match' callback we prefer to call it first, and
if it fails to find matching endpoint, then we try to use default matching
algorithm.
Signed-off-by: NRobert Baldyga <r.baldyga@samsung.com>
Signed-off-by: NFelipe Balbi <balbi@ti.com>