bus: mvebu-mbus: Add static window allocation to the DT binding

This patch adds static window allocation to the device tree binding.
Each first-child of the mbus-compatible node, with a suitable 'ranges'
property, declaring an address translation, will trigger an address
decoding window allocation.

Signed-off-by: Ezequiel Garcia <ezequiel.garcia@free-electrons.com>
Tested-by: Andrew Lunn <andrew@lunn.ch>
Tested-by: Sebastian Hesselbarth <sebastian.hesselbarth@gmail.com>
Signed-off-by: Jason Cooper <jason@lakedaemon.net>