drm/i915: don't enable autosuspend on platforms without RPM support

pm_runtime_{use,dont_use}_autosuspend() controls whether the device's
sysfs power/autosuspend_delay_ms file is writeable or returns -EIO on
access to user space. Since

commit 25b181b46e4340f69793a886f2cd46608487783b
Author: Imre Deak <imre.deak@intel.com>
Date:   Thu Dec 17 13:44:56 2015 +0200

  drm/i915: get a permanent RPM reference on platforms w/o RPM support

this sysfs file is writeable also on platforms without RPM support, but
userspace (at least IGT) depends on this file being unchangable to
determine whether the device supports runtime PM at all. So restore the
old behavior.

This gets rid of igt/pm_rpm failures on old platforms without RPM
support, where the test should be skipped.

Testcase: igt/pm_rpm/basic-rte
Signed-off-by: Imre Deak <imre.deak@intel.com>
Reviewed-by: David Weinehall <david.weinehall@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1450371873-878-1-git-send-email-imre.deak@intel.com

drivers/gpu/drm/i915/intel_runtime_pm.c

@@ -2309,18 +2309,21 @@ void intel_runtime_pm_enable(struct drm_i915_private *dev_priv)
 	struct drm_device *dev = dev_priv->dev;
 	struct device *device = &dev->pdev->dev;
 
+	pm_runtime_set_autosuspend_delay(device, 10000); /* 10s */
+	pm_runtime_mark_last_busy(device);
+
 	/*
 	 * Take a permanent reference to disable the RPM functionality and drop
 	 * it only when unloading the driver. Use the low level get/put helpers,
 	 * so the driver's own RPM reference tracking asserts also work on
 	 * platforms without RPM support.
 	 */
-	if (!HAS_RUNTIME_PM(dev))
+	if (!HAS_RUNTIME_PM(dev)) {
+		pm_runtime_dont_use_autosuspend(device);
 		pm_runtime_get_sync(device);
-
-	pm_runtime_set_autosuspend_delay(device, 10000); /* 10s */
-	pm_runtime_mark_last_busy(device);
-	pm_runtime_use_autosuspend(device);
+	} else {
+		pm_runtime_use_autosuspend(device);
+	}
 
 	/*
 	 * The core calls the driver load handler with an RPM reference held.