usb: dwc3: ep0: make dwc3 ep0 build in uboot

*) Changed the included header files to that used in u-boot.
*) added dwc3_ep_event_string() used in ep0.c
*) Fixed other misc warnings

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