drivers: memory: Introduce Marvell EBU Device Bus driver

Marvell EBU SoCs such as Armada 370/XP, Orion5x (88f5xxx) and
Discovery (mv78xx0) supports a Device Bus controller to access several
kinds of memories and I/O devices (NOR, NAND, SRAM, FPGA).

This commit adds a driver to handle this controller. So far only
Armada 370, Armada XP and Discovery SoCs are supported.

The driver must be registered through a device tree node;
as explained in the binding document.

For each child node in the device tree, this driver will:
  * set timing parameters
  * register a child device
  * setup an address decoding window, using the mbus driver

Keep in mind the address decoding window setup is only a temporary hack.
This code will be removed from this devbus driver as soon as a proper device
tree binding for the mbus driver is added.

Signed-off-by: Ezequiel Garcia <ezequiel.garcia@free-electrons.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Jason Cooper <jason@lakedaemon.net>