dt-bindings: net: ti,bluetooth: Convert to json-schema

Convert the Texas Instruments serial-attached bluetooth Device Tree
binding documentation to json-schema.

Add missing max-speed property.
Update the example.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Acked-by: David Lechner <david@lechnology.com>
Link: https://lore.kernel.org/r/c1814db9aff7f09ea41b562a2da305312d8df2dd.1634646975.git.geert+renesas@glider.be


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