dt-bindings: net: dsa: dt bindings for microchip lan937x

Documentation in .yaml format and updates to the MAINTAINERS
Also 'make dt_binding_check' is passed.

RGMII internal delay values for the mac is retrieved from
rx-internal-delay-ps & tx-internal-delay-ps as per the feedback from
v3 patch series.
https://lore.kernel.org/netdev/20210802121550.gqgbipqdvp5x76ii@skbuf/



It supports only the delay value of 0ns and 2ns.

Signed-off-by: Prasanna Vengateshan <prasanna.vengateshan@microchip.com>
Signed-off-by: Arun Ramadoss <arun.ramadoss@microchip.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>