image-fdt: save no-map parameter of reserve-memory

Save the 'no-map' information present in 'reserved-memory' node to allow
correct handling when the MMU is configured in board to avoid
speculative access.

This binding is defined in
doc/device-tree-bindings/reserved-memory/reserved-memory.txt

Additional properties:
...
no-map (optional) - empty property
    - Indicates the operating system must not create a virtual mapping
      of the region as part of its standard mapping of system memory,
      nor permit speculative access to it under any circumstances other
      than under the control of the device driver using the region.

Signed-off-by: Patrick Delaunay <patrick.delaunay@foss.st.com>