dt-bindings: arm: socfpga: Add S10 System Manager binding

Add the device tree bindings for the Stratix10 System Manager.

Signed-off-by: Thor Thayer <thor.thayer@linux.intel.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Reviewed-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Lee Jones <lee.jones@linaro.org>