usb: dwc3: gadget: make dwc3 gadget build in uboot

usb: dwc3: gadget: make dwc3 gadget build in uboot

Did a bunch of things to get dwc3/gadget.c compile in u-boot without
build errors and warnings
*) Changed the included header files to that used in u-boot.
*) Used dma_alloc_coherent and dma_free_coherent APIs of u-boot
*) removed sg support
*) remove jiffies and used a simple while loop
*) removed irq support and added a function to call these interrupt handler.

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