dt-bindings: reserved-memory: Introduce memory-region-names

In order to make the reserved-memory bindings more consistent with other
existing bindings, add a memory-region-names property that contains an
array of strings that name the entries of the memory-region property and
allows these regions to be looked up by name.
Signed-off-by: Thierry Reding <treding@nvidia.com>
Signed-off-by: Rob Herring <robh@kernel.org>

Documentation/devicetree/bindings/reserved-memory/reserved-memory.txt

@@ -77,6 +77,8 @@ Regions in the /reserved-memory node may be referenced by other device
 nodes by adding a memory-region property to the device node.
 
 memory-region (optional) - phandle, specifier pairs to children of /reserved-memory
+memory-region-names (optional) - a list of names, one for each corresponding
+  entry in the memory-region property
 
 Example
 -------