board: ti: AM43xx: added USB initializtion code

Implemented board_usb_init(), board_usb_cleanup() and
usb_gadget_handle_interrupts() in am43xx board file that
can be invoked by various gadget drivers.

Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>
Reviewed-by: Lukasz Majewski <l.majewski@samsung.com>
2 files changed