cpuidle: dt_idle_genpd: Add helper function to remove genpd topology

Genpd parent and child domain topology created using dt_idle_pd_init_topology()
needs to be removed during error cases.

Add new helper function dt_idle_pd_remove_topology() for same.

Cc: stable@vger.kernel.org
Reviewed-by: Ulf Hanssson <ulf.hansson@linaro.org>
Signed-off-by: Maulik Shah <quic_mkshah@quicinc.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>