The OMAP3 supports uploading the first stage bootloader via USB.
The ROM leaves the MUSB controller enabled and it can then be used
to upload a 2nd stage image. This patch adds the omap3-usb-loader tool
and the necessary barebox support to upload the 2nd stage image.

The omap usb loader tool is downloaded from https://github.com/grant-h/omap_loader
and changed to also accept CHSETTINGS images.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>