net: phy: Add Broadcom BCM53xx switch driver

net: phy: Add Broadcom BCM53xx switch driver

Add a minimalistic Broadcom BCM53xx (roboswitch) switch driver similar
to the Marvell MV88E617x. This takes care of configuring the minimum
amount out of the switch hardware such that each user visible port
(configurable) and the CPU port can forward packets between each other
while preserving isolation with other ports.

This is useful for e.g: the Lamobo R1 board featuring a Broadcom
BCM53125 switch.

Reviewed-by: Stefan Roese <sr@denx.de>
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>