dt-bindings: clock: axg-audio: unexpose controller inputs

Remove the bindings ID of the clock input of the controller. These
clocks are purely internal to the controller, exposing them was a
mistake. Actually, these should not even be in the provider and have
IDs to begin with.

Unexpose these IDs before:
 * someone starts using them (even if there no valid reason to do so)
 * the actual clocks are removed. The fact that they exist is just the
   result of an ugly hack. This will be resolved in CCF when we can
   reference DT directly in parent table.

Signed-off-by: Jerome Brunet <jbrunet@baylibre.com>
Acked-by: Maxime Jourdan <mjourdan@baylibre.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
Link: https://lkml.kernel.org/r/20190213095835.17448-1-jbrunet@baylibre.com