greybus: svc: Replace link config hack with standard operation

The link config operation was a hack only designed to fulfill the camera
driver's needs. Now that a standard operation is defined for the same
purpose, implement it and remove the hack.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>