edtlib: amend PropertySpec.path API documentation

[dottspina]

PropertySpec.path does not tell "the file where the property was last modified", but instead the binding file specifying the devicetree node of which this is a property.

This is a known issue (#65135), which we thought was fixed (#65221). The solution turned out to be incorrect, and we reverted the patch (#80030).

This PR aims to definitively close #65135 by simply amending the API documentation: edtlib: amend PropertySpec.path API documentation.

While writing this PR, I came across another wording that I found confusing (class edtlib.Node):

    props:
      A dict that maps property names to Property objects.
      Property objects are created for all devicetree properties on the node
      that are mentioned in 'properties:' in the binding.

AFAICT, assuming that "mentioned in 'properties:' in the binding" refers to properties whose specification we find in Node._binding.prop2specs, node properties are created only for those that actually have a value (a default value from the binding, or an explicit value from the DTS).
And usually a node has fewer properties than its binding defines (supports), literally len(node._binding.prop2specs) > len(node.props).
If the above reasoning is correct, then the API documentation seems confusing to me: the additional commit, edtlib: amend Node.props API documentation, is about that.

Thanks

Fixes #65135.