ARM: dts: Cygnus: Add the ethernet switch and ethernet PHY

Cygnus has a single amac controller connected to the B53 switch with 2
PHYs. On the BCM911360_EP platform, those two PHYs are connected to the
external ethernet jacks.

Signed-off-by: Eric Anholt <eric@anholt.net>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>