usb: gadget: allow ci_udc to build with new gadget framework

Allow ci_udc.o to be built when using the new(?) USB gadget framework,
as enabled by CONFIG_USB_GADGET.

Note that this duplicates the Makefile entry for ci_udc.o, since it's
also included inside #ifdef CONFIG_USB_ETHER. I'm not sure what that
define means; perhaps an old style of Ethernet-specific USB gadget
implementation?

I wonder if the line that this patch adds shouldn't be outside all of
the ifdefs, so it stands on its own, similar to how e.g. epautoconf.o
is shared between the two?

Signed-off-by: Stephen Warren <swarren@nvidia.com>