Partially revert "drm/i915: s/mdelay/msleep/" in ilk rps code

This reverts commit 6adfb1ef.

Ironlake RPS code runs under an irqsave spinlock and hence sleeping
isn't allowed. Not a this long delay while blocking irqs isn't great
at all, but fixing the locking scheme is a lot more involved.

So just revert for now.

Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reported-by: kernel test robot <ying.huang@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>

drivers/gpu/drm/i915/intel_pm.c

@@ -4266,7 +4266,7 @@ static void ironlake_enable_drps(struct drm_device *dev)
 
 	if (wait_for_atomic((I915_READ(MEMSWCTL) & MEMCTL_CMD_STS) == 0, 10))
 		DRM_ERROR("stuck trying to change perf mode\n");
-	msleep(1);
+	mdelay(1);
 
 	ironlake_set_drps(dev, fstart);
 
@@ -4297,10 +4297,10 @@ static void ironlake_disable_drps(struct drm_device *dev)
 
 	/* Go back to the starting frequency */
 	ironlake_set_drps(dev, dev_priv->ips.fstart);
-	msleep(1);
+	mdelay(1);
 	rgvswctl |= MEMCTL_CMD_STS;
 	I915_WRITE(MEMSWCTL, rgvswctl);
-	msleep(1);
+	mdelay(1);
 
 	spin_unlock_irq(&mchdev_lock);
 }