bus: uniphier-system-bus: add UniPhier System Bus driver

The UniPhier System Bus is an external bus that connects on-board
devices to the UniPhier SoC.  Each bank (chip select) is dynamically
mapped to the CPU-viewed address base via the bus controller.  The
bus controller must be configured before any access to the bus.

This driver parses the "ranges" property of the System Bus node and
initialized the bus controller.  After the bus becomes ready, devices
below it are populated.

Note:
Each bank can be mapped anywhere in the supported address space;
there is nothing preventing us from assigning bank 0 on 0x42000000,
0x43000000, or anywhere as long as such region is not used by others.
So, the "ranges" is just one possible software configuration, which
does not seem to fit in device tree because device tree is a hardware
description language.  However, of_translate_address() requires
"ranges" in every bus node between CPUs and device mapped on the CPU
address space.  In other words, "ranges" properties must be statically
defined in device tree.  After some discussion, I decided the dynamic
address reassignment by the driver is too bothersome.  Instead, the
device tree should provide a reasonable translation setup that the OS
can rely on.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Acked-by: Rob Herring <robh@kernel.org>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Olof Johansson <olof@lixom.net>

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