dt-bindings: display: msm: gmu: move sram property to gpu bindings

The sram property was incorrectly added to the GMU binding when it
really belongs with the GPU binding instead. Let's go ahead and
move it.

While changes are being made here, let's update the sram property
description to mention that this property is only valid for a3xx and
a4xx GPUs. The a3xx/a4xx example in the GPU is replaced with what was
in the GMU.

Signed-off-by: Brian Masney <masneyb@onstation.org>
Fixes: 198a72c8 ("dt-bindings: display: msm: gmu: add optional ocmem property")
Acked-by: Jordan Crouse <jcrouse@codeaurora.org>
Signed-off-by: Rob Clark <robdclark@chromium.org>