dt-bindings: clk: emev2: Convert to json-schema

Convert the Renesas EMMA Mobile EV2 System Management Unit (SMU) Device
Tree binding documentation to json-schema.

Drop the separate provider examples, as they mostly duplicate the global
example.  Drop the consumer example, as it doesn't belong here.
Update the global example to match reality.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/r/526e1a412145a0fcc5a43dcf6de5c580301017cb.1620119350.git.geert+renesas@glider.be


Signed-off-by: Rob Herring <robh@kernel.org>