arm64: dts: marvell: add Device Tree files for Armada 7K/8K

arm64: dts: marvell: add Device Tree files for Armada 7K/8K

This commit adds the base Device Tree files for the Armada 7K and 8K
SoCs, as well as the Armada 8040 DB board.

The Armada 7020, 7040 (7K family) and 8020, 8040 (8K family) are
composed of:

 - An AP806 block that contains the CPU core and a few basic
   peripherals. The AP806 is available in dual core configurations
   (used in 7020 and 8020) and quad core configurations (used in 8020
   and 8040).

 - One or two CP110 blocks that contain all the high-speed interfaces
   (SATA, PCIe, Ethernet, etc.). The 7K family chips have one CP110,
   and the 8K family chips have two CP110, giving them twice the
   number of HW interfaces.

In order to represent this from a Device Tree point of view, this
commit creates the following hierarchy:

 * armada-ap806.dtsi - definitions common to dual/quad ap806
   * armada-ap806-dual.dtsi - description of the two CPUs
     * armada-7020.dtsi - description of the 7020 SoC
     * armada-8020.dtsi - description of the 8020 SoC
   * armada-ap806-quad.dtsi - description of the four CPUs
     * armada-7040.dtsi - description of the 7040 SoC
       * armada-7040-db.dts - description of the 7040 board
     * armada-8040.dtsi - description of the 8040 SoC

The CP110 blocks are not described yet, and will be part of future
patch series.

[gregory.clement@free-electrons.com: Fix commit title by adding ' dts:']
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Gregory CLEMENT <gregory.clement@free-electrons.com>