agp/intel: use correct GTT offset on VLV

VLV is a gen7 device, but we don't currently handle that in the switch.
So add it and write the PTEs correctly.

Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/char/agp/intel-gtt.c

diff --git a/drivers/char/agp/intel-gtt.c b/drivers/char/agp/intel-gtt.c
index 692610e..9ed92ef 100644
--- a/drivers/char/agp/intel-gtt.c
+++ b/drivers/char/agp/intel-gtt.c
@@ -1253,6 +1253,7 @@
 		switch (INTEL_GTT_GEN) {
 		case 5:
 		case 6:
+		case 7:
 			gtt_offset = MB(2);
 			break;
 		case 4: