memory: add ARM PL172 MultiPort Memory Controller driver

This driver makes it possible to configure the static memory
chip selects on the ARM PL172 MultiPort Memory Controller
from a set of properties in DT. Configuration of dynamic
memory is not supported and is left to the boot loader.

The intended usage is to setup timing and configuration for
static memory devices like NAND and NOR Flash before they
are probed by a driver.

Signed-off-by: Joachim Eastwood <manabian@gmail.com>
Signed-off-by: Olof Johansson <olof@lixom.net>