Add support for the A750 GPU found on the SM8650 platform

Unlike the the very close A740 GPU on the SM8550 SoC, the A750 GPU
doesn't have an HWCFG block but a separate register set.

The A750 GPU info are added under the adreno_is_a750() macro and
the ADRENO_7XX_GEN3 family id.
Reviewed-by: Konrad Dybcio <konrad.dybcio@linaro.org>
Signed-off-by: Neil Armstrong <neil.armstrong@linaro.org>
Patchwork: https://patchwork.freedesktop.org/patch/578693/Signed-off-by: Rob Clark <robdclark@chromium.org>