The A20 has a few SRAM that can be mapped either to a device or to the CPU,
with the mapping being controlled by a SRAM controller.

Add the SRAM controller, the SRAM that it drives and the section that can
be used by the various devices.
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Hans de Goede <hdegoede@redhat.com>
Tested-by: Hans de Goede <hdegoede@redhat.com>