cpuidle: psci: Drop redundant sync_state support

cpuidle: psci: Drop redundant sync_state support

The recent updates to the genpd core, can entirely manage the sync_state
support for the cpuidle-psci-domain. More precisely, genpd prevents our
->power_off() callback from being invoked, until all of our consumers are
ready for it.

Let's therefore drop the sync_state support for the cpuidle-psci-domain as
it has become redundant.

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/20250701114733.636510-24-ulf.hansson@linaro.org