pmdomain: core: Prepare to add the common ->sync_state() support

Before we can implement the common ->sync_state() support in genpd, we need
to allow a few specific genpd providers to opt out from the new behaviour.

Let's introduce GENPD_FLAG_NO_SYNC_STATE as a new genpd config option, to
allow providers to opt out.

Suggested-by: Saravana Kannan <saravanak@google.com>
Tested-by: Hiago De Franco <hiago.franco@toradex.com> # Colibri iMX8X
Tested-by: Tomi Valkeinen <tomi.valkeinen@ideasonboard.com> # TI AM62A,Xilinx ZynqMP ZCU106
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
Link: https://lore.kernel.org/r/20250701114733.636510-9-ulf.hansson@linaro.org