drivers: soc: sunxi: Introduce SoC driver to map SRAMs

The Allwinner SoCs have a handful of SRAM that can be either mapped to be
accessible by devices or the CPU.

That mapping is controlled by an SRAM controller, and that mapping might
not be set by the bootloader, for example if the device wasn't used at all,
or if we're using solutions like the U-Boot's Falcon Boot.

We could also imagine changing this at runtime for example to change the
mapping of these SRAMs to use them for suspend/resume or runtime memory
rate change, if that ever happens.

These use cases require some API in the kernel to control that mapping,
exported through a drivers/soc driver.

This driver also implement a debugfs file that shows the SRAM found in the
system, the current mapping and the SRAM that have been claimed by some
drivers in the kernel.

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 <hdegoed...