net: dsa: b53: Add support for Broadcom Omega SoC internal switch

Add support for the Broadcom Omega SoC internal ethernet switch
to the b53 srab driver in the DSA framework.

Signed-off-by: Arun Parameswaran <arun.parameswaran@broadcom.com>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>