dt-bindings: bus: add device tree bindings for qcom,ssc-block-bus

Adds bindings for the AHB bus which exposes the SSC block in the global
address space. This bus (and the SSC block itself) is present on certain
qcom SoCs.

In typical configuration, this bus (as some of the clocks and registers
that we need to manipulate) is not accessible to the OS, and the
resources on this bus are indirectly accessed by communicating with a
hexagon CPU core residing in the SSC block. In this configuration, the
hypervisor is the one performing the bus initialization for the purposes
of bringing the haxagon CPU core out of reset.

However, it is possible to change the configuration, in which case this
binding serves to allow the OS to initialize the bus.

Signed-off-by: Michael Srba <Michael.Srba@seznam.cz>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Link: https://lore.kernel.org/r/20220411072156.24451-4-michael.srba@seznam.cz