firmware: arm_scmi: Add SCMI PM driver remove routine

Currently, when removing the SCMI PM driver not all the resources
registered with genpd subsystem are properly de-registered.

As a side effect of this after a driver unload/load cycle you get a
splat with a few warnings like this:

 | debugfs: Directory 'BIG_CPU0' with parent 'pm_genpd' already present!
 | debugfs: Directory 'BIG_CPU1' with parent 'pm_genpd' already present!
 | debugfs: Directory 'LITTLE_CPU0' with parent 'pm_genpd' already present!
 | debugfs: Directory 'LITTLE_CPU1' with parent 'pm_genpd' already present!
 | debugfs: Directory 'LITTLE_CPU2' with parent 'pm_genpd' already present!
 | debugfs: Directory 'LITTLE_CPU3' with parent 'pm_genpd' already present!
 | debugfs: Directory 'BIG_SSTOP' with parent 'pm_genpd' already present!
 | debugfs: Directory 'LITTLE_SSTOP' with parent 'pm_genpd' already present!
 | debugfs: Directory 'DBGSYS' with parent 'pm_genpd' already present!
 | debugfs: Directory 'GPUTOP' with parent 'pm_genpd' already present!

Add a proper scmi_pm_domain_remove callback to the driver in order to
take care of all the needed cleanups not handled by devres framework.

Link: https://lore.kernel.org/r/20220817172731.1185305-7-cristian.marussi@arm.com
Signed-off-by: Cristian Marussi <cristian.marussi@arm.com>
Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>

drivers/firmware/arm_scmi/scmi_pm_domain.c

@@ -138,9 +138,28 @@ static int scmi_pm_domain_probe(struct scmi_device *sdev)
 	scmi_pd_data->domains = domains;
 	scmi_pd_data->num_domains = num_domains;
 
+	dev_set_drvdata(dev, scmi_pd_data);
+
 	return of_genpd_add_provider_onecell(np, scmi_pd_data);
 }
 
+static void scmi_pm_domain_remove(struct scmi_device *sdev)
+{
+	int i;
+	struct genpd_onecell_data *scmi_pd_data;
+	struct device *dev = &sdev->dev;
+	struct device_node *np = dev->of_node;
+
+	of_genpd_del_provider(np);
+
+	scmi_pd_data = dev_get_drvdata(dev);
+	for (i = 0; i < scmi_pd_data->num_domains; i++) {
+		if (!scmi_pd_data->domains[i])
+			continue;
+		pm_genpd_remove(scmi_pd_data->domains[i]);
+	}
+}
+
 static const struct scmi_device_id scmi_id_table[] = {
 	{ SCMI_PROTOCOL_POWER, "genpd" },
 	{ },
@@ -150,6 +169,7 @@ MODULE_DEVICE_TABLE(scmi, scmi_id_table);
 static struct scmi_driver scmi_power_domain_driver = {
 	.name = "scmi-power-domain",
 	.probe = scmi_pm_domain_probe,
+	.remove = scmi_pm_domain_remove,
 	.id_table = scmi_id_table,
 };
 module_scmi_driver(scmi_power_domain_driver);