ARM: dts: qcom: msm8974: rename GPU's OPP table node

Rename the GPU's opp table node to make it follow the
display/msm/gpu.yaml schema.

Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Link: https://lore.kernel.org/r/20220706145412.1566011-6-dmitry.baryshkov@linaro.org