usb: dwc3: remove dwc3 dependency on host AND gadget.

DWC3 controller curretly depends on USB && USB_GADGET.
Some hardware may like to use only host feature on dwc3,
or only gadget feature.

So, removing this dependency of USB_DWC3 on USB and USB_GADGET.
Adding the mode of operaiton of DWC3 also here
HOST/GADGET/DUAL_ROLE based on which features are enabled.

[ balbi@ti.com :
	. make sure we have default modes for all possible Kernel
		configurations.
	. Remove the config -> menuconfig change as it's unnecessary
	. switch over to IS_ENABLED() ]

CC: Doug Anderson <dianders@chromium.org>
Signed-off-by: Vivek Gautam <gautam.vivek@samsung.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>