ARM: dts: BCM53573: Describe on-SoC BCM53125 rev 4 switch

[ Upstream commit 9fb90ae6 ]

BCM53573 family SoC have Ethernet switch connected to the first Ethernet
controller (accessible over MDIO).

Signed-off-by: Rafał Miłecki <rafal@milecki.pl>
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Stable-dep-of: 05d2c3d5 ("ARM: dts: BCM53573: Drop nonexistent #usb-cells")
Signed-off-by: Sasha Levin <sashal@kernel.org>