dm: usb: udc: Factor out plain udevice handler functions

Pull the functionality of UDC uclass that operates on plain udevice
and does not use this dev_array array into separate functions and
expose those functions, so that as much code as possible can be
switched over to these functions and the dev_array can be dropped.

Reviewed-by: Mattijs Korpershoek <mkorpershoek@baylibre.com>
Signed-off-by: Marek Vasut <marex@denx.de>