dt-bindings: display/msm: gpu: Document GMU wrapper-equipped A6xx

dt-bindings: display/msm: gpu: Document GMU wrapper-equipped A6xx

The "GMU Wrapper" is Qualcomm's name for "let's treat the GPU blocks
we'd normally assign to the GMU as if they were a part of the GMU, even
though they are not". It's a (good) software representation of the GMU_CX
and GMU_GX register spaces within the GPUSS that helps us programatically
treat these de-facto GMU-less parts in a way that's very similar to their
GMU-equipped cousins, massively saving up on code duplication.

The "wrapper" register space was specifically designed to mimic the layout
of a real GMU, though it rather obviously does not have the M3 core et al.

GMU wrapper-equipped A6xx GPUs require clocks and clock-names to be
specified under the GPU node, just like their older cousins. Account
for that.

Acked-by: Rob Herring <robh@kernel.org>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Konrad Dybcio <konrad.dybcio@linaro.org>
Patchwork: https://patchwork.freedesktop.org/patch/542748/
Signed-off-by: Rob Clark <robdclark@chromium.org>