clk: qcom: gdsc: Support 'synced_poweroff' genpd flag

Add support for the newly added 'synced_poweroff' genpd flag. This allows
some clients (like adreno gpu driver) to request gdsc driver to ensure
a votable gdsc (like gpucc cx gdsc) has collapsed at hardware.

Signed-off-by: Akhil P Oommen <quic_akhilpo@quicinc.com>
Reviewed-by: Ulf Hansson <ulf.hansson@linaro.org>
Signed-off-by: Bjorn Andersson <andersson@kernel.org>
Link: https://lore.kernel.org/r/20230102161757.v5.2.Ic128c1df50b7fc9a6b919932a3b41a799b5ed5e8@changeid