drm/radeon/kms: fix tiling reg on fusion

The location of MC_ARB_RAMCFG changed on fusion.
I've diffed all the other regs in evergreend.h and this
is the only other reg that changed.

Signed-off-by: Alex Deucher <alexdeucher@gmail.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>
diff --git a/drivers/gpu/drm/radeon/evergreen.c b/drivers/gpu/drm/radeon/evergreen.c
index c20eac3..9073e3b 100644
--- a/drivers/gpu/drm/radeon/evergreen.c
+++ b/drivers/gpu/drm/radeon/evergreen.c
@@ -1780,7 +1780,10 @@
 
 
 	mc_shared_chmap = RREG32(MC_SHARED_CHMAP);
-	mc_arb_ramcfg = RREG32(MC_ARB_RAMCFG);
+	if (rdev->flags & RADEON_IS_IGP)
+		mc_arb_ramcfg = RREG32(FUS_MC_ARB_RAMCFG);
+	else
+		mc_arb_ramcfg = RREG32(MC_ARB_RAMCFG);
 
 	switch (rdev->config.evergreen.max_tile_pipes) {
 	case 1: