dt-bindings: arm: keystone: Add common TI SCI bindings

Add a bindings document that defines the common TI SCI properties
used by various K3 device management nodes such as clock controllers,
interrupt controllers, reset controllers or remoteproc devices.

The required properties for each device management node shall be
specified in the respective binding document.

Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Suman Anna <s-anna@ti.com>
Link: https://lore.kernel.org/r/20200721223617.20312-2-s-anna@ti.com


Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>