drm/msm/adreno: adreno_gpu: Don't set OPP scaling clock w/ GMU

Recently I contributed the switch to OPP API for all Adreno generations.
I did however also skip over the fact that GPUs with a GMU don't specify
a core clock of any kind in the GPU node. While that didn't break
anything, it did introduce unwanted spam in the dmesg:

adreno 5000000.gpu: error -ENOENT: _opp_set_clknames: Couldn't find clock with name: core_clk

Guard the entire logic so that it's not used with GMU-equipped GPUs.

Fixes: 9f251f93

 ("drm/msm/adreno: Use OPP for every GPU generation")
Signed-off-by: Konrad Dybcio <konrad.dybcio@linaro.org>
Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Patchwork: https://patchwork.freedesktop.org/patch/530347/
Link: https://lore.kernel.org/r/20230223-topic-gmuwrapper-v6-1-2034115bb60c@linaro.org
Signed-off-by: Rob Clark <robdclark@chromium.org>