kernel: usb.mk: enable chipidea udc mode

The chipidea USB OTG controller is dual-role and supports both host and device
modes. Enable device mode.

Tested on Gateworks Ventana imx6 board with g_ether.

Are there any other targets out there that use the CHIPIDEA controller? If so
testing is needed for those.

Signed-off-by: Tim Harvey <tharvey@gateworks.com>

SVN-Revision: 40905