drm/radeon/kms: Use radeon_agp_disable when disabling AGP

Use same common function to disable agp so we replace the GART
callback by the proper one when we do so. This fix oops if
radeon_agp_init report failure.

This patch also move radeon_agp_init out of *_mc_init for r600
& rv770 so that we can have a similar behavior than for previous
hw, ie if agp_init fails it will fallback to GPU GART and disable
AGP.

Signed-off-by: Jerome Glisse <jglisse@redhat.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>
diff --git a/drivers/gpu/drm/radeon/radeon.h b/drivers/gpu/drm/radeon/radeon.h
index eb5f99b..ab37dd0 100644
--- a/drivers/gpu/drm/radeon/radeon.h
+++ b/drivers/gpu/drm/radeon/radeon.h
@@ -1017,6 +1017,8 @@
 #define radeon_hpd_set_polarity(rdev, hpd) (rdev)->asic->hpd_set_polarity((rdev), (hpd))
 
 /* Common functions */
+/* AGP */
+extern void radeon_agp_disable(struct radeon_device *rdev);
 extern int radeon_gart_table_vram_pin(struct radeon_device *rdev);
 extern int radeon_modeset_init(struct radeon_device *rdev);
 extern void radeon_modeset_fini(struct radeon_device *rdev);