dt-bindings: net: dsa: realtek-smi: document new compatible rtl8365mb

rtl8365mb is a new realtek-smi subdriver for the RTL8365MB-VC 4+1 port
10/100/1000M Ethernet switch controller. Its compatible string is
"realtek,rtl8365mb".

Signed-off-by: Alvin Šipraga <alsi@bang-olufsen.dk>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Acked-by: Rob Herring <robh@kernel.org>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: David S. Miller <davem@davemloft.net>