dt-bindings: net: can: Document transceiver implementation as phy

Some transceivers need a configuration step (for example, pulling the
standby or enable lines) for them to start sending messages. The
transceiver can be implemented as a phy with the configuration done in
the phy driver. The bit rate limitation can the be obtained by the
driver using the phy node.

Document the above implementation in the bosch mcan bindings.

Link: https://lore.kernel.org/r/20210510052541.14168-2-a-govindraju@ti.com
Signed-off-by: Faiz Abbas <faiz_abbas@ti.com>
Signed-off-by: Aswath Govindraju <a-govindraju@ti.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>

Documentation/devicetree/bindings/net/can/bosch,m_can.yaml

@@ -107,6 +107,9 @@ properties:
   can-transceiver:
     $ref: can-transceiver.yaml#
 
+  phys:
+    maxItems: 1
+
 required:
   - compatible
   - reg