drm/msm/a6xx: Use genpd notifier to ensure cx-gdsc collapse

As per the recommended recovery sequence of adreno gpu, cx gdsc should
collapse at hardware before it is turned back ON. This helps to clear
out the stale states in hardware before it is reinitialized. Use the
genpd notifier along with the newly introduced
dev_pm_genpd_synced_poweroff() api to ensure that cx gdsc has collapsed
before we turn it back ON.

Signed-off-by: Akhil P Oommen <quic_akhilpo@quicinc.com>
Reviewed-by: Ulf Hansson <ulf.hansson@linaro.org>
Patchwork: https://patchwork.freedesktop.org/patch/516472/
Link: https://lore.kernel.org/r/20230102161757.v5.5.I9e10545c6a448d5eb1b734839b871d1b3146dac3@changeid
Signed-off-by: Rob Clark <robdclark@chromium.org>