dt-bindings: net: renesas-ravb: Make stream buffer optional

dt-bindings: net: renesas-ravb: Make stream buffer optional

The Stream Buffer for EtherAVB-IF (STBE) is an optional component, and
is not present on all SoCs.

Document this in the DT bindings, including a list of SoCs that do have
it.

Fixes: 785ec87483d1e24a ("ravb: document R8A77970 bindings")
Fixes: f231c4178a655b09 ("dt-bindings: net: renesas-ravb: Add support for R8A77995 RAVB")
Signed-off-by: Geert Uytterhoeven <[email protected]>
Reviewed-by: Simon Horman <[email protected]>
Acked-by: Sergei Shtylyov <[email protected]>
Reviewed-by: Rob Herring <[email protected]>
Signed-off-by: David S. Miller <[email protected]>