usb: gadget: mtu3: Convert interrupt handling to usb_gadget_generic_ops

usb: gadget: mtu3: Convert interrupt handling to usb_gadget_generic_ops

Implement .handle_interrupts callback as a replacement for deprecated
dm_usb_gadget_handle_interrupts() function. The new callback allows
for each DM capable USB gadget controller driver to define its own
IRQ handling implementation without colliding with other controller
drivers.

Signed-off-by: Marek Vasut <marek.vasut+renesas@mailbox.org>
Reviewed-by: Mattijs Korpershoek <mkorpershoek@baylibre.com>
Tested-by: Mattijs Korpershoek <mkorpershoek@baylibre.com> # vim3
Link: https://lore.kernel.org/r/20240614005309.34433-7-marek.vasut+renesas@mailbox.org
Signed-off-by: Mattijs Korpershoek <mkorpershoek@baylibre.com>