PM / Runtime: Rework the "runtime idle" helper routine

The "runtime idle" helper routine, rpm_idle(), currently ignores
return values from .runtime_idle() callbacks executed by it.
However, it turns out that many subsystems use
pm_generic_runtime_idle() which checks the return value of the
driver's callback and executes pm_runtime_suspend() for the device
unless that value is not 0.  If that logic is moved to rpm_idle()
instead, pm_generic_runtime_idle() can be dropped and its users
will not need any .runtime_idle() callbacks any more.

Moreover, the PCI, SCSI, and SATA subsystems' .runtime_idle()
routines, pci_pm_runtime_idle(), scsi_runtime_idle(), and
ata_port_runtime_idle(), respectively, as well as a few drivers'
ones may be simplified if rpm_idle() calls rpm_suspend() after 0 has
been returned by the .runtime_idle() callback executed by it.

To reduce overall code bloat, make the changes described above.

Tested-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Tested-by: Kevin Hilman <khilman@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Acked-by: Kevin Hilman <khilman@linaro.org>
Reviewed-by: Ulf Hansson <ulf.hansson@linaro.org>
Acked-by: Alan Stern <stern@rowland.harvard.edu>
diff --git a/drivers/mfd/ab8500-gpadc.c b/drivers/mfd/ab8500-gpadc.c
index 13f7866..3598b0e 100644
--- a/drivers/mfd/ab8500-gpadc.c
+++ b/drivers/mfd/ab8500-gpadc.c
@@ -886,12 +886,6 @@
 	return ret;
 }
 
-static int ab8500_gpadc_runtime_idle(struct device *dev)
-{
-	pm_runtime_suspend(dev);
-	return 0;
-}
-
 static int ab8500_gpadc_suspend(struct device *dev)
 {
 	struct ab8500_gpadc *gpadc = dev_get_drvdata(dev);
@@ -1039,7 +1033,7 @@
 static const struct dev_pm_ops ab8500_gpadc_pm_ops = {
 	SET_RUNTIME_PM_OPS(ab8500_gpadc_runtime_suspend,
 			   ab8500_gpadc_runtime_resume,
-			   ab8500_gpadc_runtime_idle)
+			   NULL)
 	SET_SYSTEM_SLEEP_PM_OPS(ab8500_gpadc_suspend,
 				ab8500_gpadc_resume)