board: STiH410-B2260: add fastboot support

Add usb_gadget_handle_interrupts(), board_usb_init(),
board_usb_cleanup() and g_dnl_board_usb_cable_connected()
callbacks needed for FASTBOOT support

Signed-off-by: Patrice Chotard <patrice.chotard@st.com>
Reviewed-by: Simon Glass <sjg@chromium.org>