drm/radeon/kms: Disable agp only if we are dealing with an AGP GPU

On IGP if you pass option agpmode=-1 you would overwrite the set_page
function callback with improper function which endup in non functioning
hw. This patch will disable agp when giving agpmode=-1 parameter only
if we are dealing with an AGP GPU.
Signed-off-by: NJerome Glisse <jglisse@redhat.com>
Signed-off-by: NDave Airlie <airlied@redhat.com>

drivers/gpu/drm/radeon/radeon_device.c

@@ -553,7 +553,7 @@ int radeon_device_init(struct radeon_device *rdev,
 		return r;
 	}
 
-	if (radeon_agpmode == -1) {
+	if (rdev->flags & RADEON_IS_AGP && radeon_agpmode == -1) {
 		radeon_agp_disable(rdev);
 	}