drm/radeon/kms: disable D1VGA and D2VGA if enabled

Once kms is enabled we don't need these, and it causes a problem
with the Lenovo W500 ACPI brightness implementation, it hangs
in a loop inside an SMI.

Signed-off-by: Dave Airlie <airlied@redhat.com>
diff --git a/drivers/gpu/drm/radeon/rv515.c b/drivers/gpu/drm/radeon/rv515.c
index 41a34c2..03c052d 100644
--- a/drivers/gpu/drm/radeon/rv515.c
+++ b/drivers/gpu/drm/radeon/rv515.c
@@ -137,6 +137,8 @@
 
 void rv515_vga_render_disable(struct radeon_device *rdev)
 {
+	WREG32(R_000330_D1VGA_CONTROL, 0);
+	WREG32(R_000338_D2VGA_CONTROL, 0);
 	WREG32(R_000300_VGA_RENDER_CONTROL,
 		RREG32(R_000300_VGA_RENDER_CONTROL) & C_000300_VGA_VSTATUS_CNTL);
 }