usb: musb: gadget: add musb_match_ep() function

Add 'match_ep' callback to utilize chip-specific knowledge in endpoint matching
process. Function does the same that was done by chip-specific code inside
of epautoconf. Now this code can be removed from there to separate generic code
from platform specific logic.

Signed-off-by: Robert Baldyga <r.baldyga@samsung.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>