memory: Add Baikal-T1 L2-cache Control Block driver

Baikal-T1 SoC provides a way to tune the MIPS P5600 CM2 L2-cache
performance up. It can be done by changing the L2-RAM Data/Tag/WS
latencies in a dedicated register exposed by the system controller.
The driver added by this commit provides a dts properties-based and
sysfs-based interface for it. The device DT node is supposed to be a
child of Baikal-T1 System Controller node.

Link: https://lore.kernel.org/r/20200526125928.17096-7-Sergey.Semin@baikalelectronics.ru


Signed-off-by: Serge Semin <Sergey.Semin@baikalelectronics.ru>
Cc: Alexey Malahov <Alexey.Malahov@baikalelectronics.ru>
Cc: Paul Burton <paulburton@kernel.org>
Cc: Olof Johansson <olof@lixom.net>
Cc: Rob Herring <robh+dt@kernel.org>
Cc: linux-mips@vger.kernel.org
Cc: soc@kernel.org
Cc: devicetree@vger.kernel.org
Signed-off-by: Arnd Bergmann <arnd@arndb.de>