[new uImage] New uImage low-level API

Add FDT-based functions for handling new format component images,
configurations, node operations, property get/set, etc.

fit_        - routines handling global new format uImage operations
              like get/set top level property, process all nodes, etc.
fit_image_  - routines handling component images subnodes
fit_conf_   - routines handling configurations node

Signed-off-by: Bartlomiej Sieka <tur@semihalf.com>
Signed-off-by: Marian Balakowicz <m8@semihalf.com>