ARM: dts: BCM53573: Add Broadcom BCM947189ACDBMR board support

Adds support for the Broadcom reference board BCM947189ACDMBR which
features the following:

* 128MB of DRAM
* External MoCA support through a Broadcom BCM6802 chip
* 1x external Gigabit PHY through the external BCM6802
* 1x USB 2.0 port
* 1x PCIE slot
* Few configurable buttons and LEDs

Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>