dt-bindings: arm: Document qcom,kpss-gcc

The ACC and GCC regions present in KPSSv1 contain registers to
control clocks and power to each Krait CPU and L2. Documenting
the bindings here.

Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>
Signed-off-by: Sricharan R <sricharan@codeaurora.org>
Tested-by: Craig Tatlor <ctatlor97@gmail.com>
Signed-off-by: Stephen Boyd <sboyd@kernel.org>