usb: udc: dwc3: Fold dwc3_uboot_handle_interrupt into dm_usb_gadget_handle_interrupts

usb: udc: dwc3: Fold dwc3_uboot_handle_interrupt into dm_usb_gadget_handle_interrupts

The only call site of dwc3_uboot_handle_interrupt() is the
dm_usb_gadget_handle_interrupts(), fold the former into the
later. This makes dwc3_uboot_handle_interrupt() unavailable
to be called from board code as well.

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/20240317044357.547037-2-marek.vasut+renesas@mailbox.org
Signed-off-by: Mattijs Korpershoek <mkorpershoek@baylibre.com>