Commit 24937c540917 ("dt-bindings: drm/msm/a6xx: Document GMU and update
GPU bindings") mistakenly omitted the GMU bindings as seen in [1].
Return them to their rightful place.

[1] https://patchwork.freedesktop.org/patch/268679/Signed-off-by: NJordan Crouse <jcrouse@codeaurora.org>
Reviewed-by: NRob Herring <robh@kernel.org>
Signed-off-by: NRob Clark <robdclark@gmail.com>