dt-bindings: can: can-transceiver: Document new binding

Add documentation to describe usage of the new can-transceiver binding.
This new binding is applicable for any CAN device therefore it exists as
its own document.

Signed-off-by: Franklin S Cooper Jr <fcooper@ti.com>
Signed-off-by: Sekhar Nori <nsekhar@ti.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Faiz Abbas <faiz_abbas@ti.com>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>