barebox-tools: add initial barebox tools support

barebox-tools: add initial barebox tools support

Add initial support to build the barebox tools for the host and the
target.

Some of the tools are generic barebox utilities (like 'bareboximd' for
image meta data inspection or 'bareboxenv' for accessing the barebox
environment) some are SoC family-specific specific utilities (like
'imx-usb-loader' or 'omap3-usb-loader').

Signed-off-by: Marco Felsch <m.felsch@pengutronix.de>
Signed-off-by: Enrico Jorns <ejo@pengutronix.de>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>