dt-bindings: display/msm/gmu: Update Adreno 623 bindings

dt-bindings: display/msm/gmu: Update Adreno 623 bindings

Update Adreno 623's dt-binding to remove smmu_clk which is not required
for this GMU.

Signed-off-by: Jie Zhang <quic_jiezh@quicinc.com>
Signed-off-by: Akhil P Oommen <quic_akhilpo@quicinc.com>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Patchwork: https://patchwork.freedesktop.org/patch/672455/
Signed-off-by: Rob Clark <robin.clark@oss.qualcomm.com>