scripts/dts/edtlib.py: Hoist enum checking before early out

Move the enum checking before we early out for '#' and '-map' properties
so they can benefit from it.  Also make the error messages for failed
'enum' check more informative by including the paths to the .dts file
and the binding for the node.

Signed-off-by: Kumar Gala <kumar.gala@linaro.org>
Signed-off-by: Ulf Magnusson <Ulf.Magnusson@nordicsemi.no>