drm/i915: fix drps disable so unload & re-load works

At unload time, we need to disable DRPS, but we need to do it correctly
or the GPU will hang and we won't be able to load the module again.  So
set the SFCAVM bit so we can properly restore the DRPS config at unload.

Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>
Signed-off-by: Eric Anholt <eric@anholt.net>

drivers/gpu/drm/i915/intel_display.c

@@ -4699,7 +4699,7 @@ void ironlake_disable_drps(struct drm_device *dev)
 	fstart = (I915_READ(MEMMODECTL) & MEMMODE_FSTART_MASK) >>
 		MEMMODE_FSTART_SHIFT;
 	rgvswctl = (MEMCTL_CMD_CHFREQ << MEMCTL_CMD_SHIFT) |
-		(fstart << MEMCTL_FREQ_SHIFT);
+		(fstart << MEMCTL_FREQ_SHIFT) | MEMCTL_SFCAVM;
 	I915_WRITE(MEMSWCTL, rgvswctl);
 	msleep(1);
 	rgvswctl |= MEMCTL_CMD_STS;