base-files: support label-property-less in get_dt_leds

base-files: support label-property-less in get_dt_leds

The LED's "label" property has been deprecated in upstream by:

|commit c5d18dd6b64e09dd6984bda9bdd55160af537a8c
|Author: Jacek Anaszewski <jacek.anaszewski@gmail.com>
|Date:   Sun Jun 9 20:19:04 2019 +0200
|
|    dt-bindings: leds: Add properties for LED name construction
|
|    Introduce dedicated properties for conveying information about
|    LED function and color. Mark old "label" property as deprecated.
|
|    Additionally function-enumerator property is being provided
|    for the cases when neither function nor color can be used
|    for LED differentiation.

in order to be somewhat prepared, this patch adds a fallback
as a last resort to make the current led code work by falling
back to the node-name as the "label".

Signed-off-by: Christian Lamparter <chunkeey@gmail.com>