imx-usb-loader: new host package

This host package allows to build tools to download and execute code on
Freescale i.MX5/i.MX6 and Vybrid SoCs through the Serial Download
Protocol.

The work behind this commit was funded by ECA Group
<http://www.ecagroup.com

>. ECA Group is the copyright owner of the
contributed code.

Signed-off-by: Antoine Tenart <antoine.tenart@free-electrons.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>