drm/i915: Add support for fence registers on Ivybridge.

The registers are the same as on Sandybridge.  Fixes scrambled display
in X when it does software drawing to the GTT, and scans the results
out as tiled.

Signed-off-by: Eric Anholt <eric@anholt.net>
Reviewed-by: Jesse Barnes <jbarnes@virtuousgeek.org>
Signed-off-by: Keith Packard <keithp@keithp.com>

drivers/gpu/drm/i915/i915_gem.c

@@ -2673,6 +2673,7 @@ i915_gem_object_get_fence(struct drm_i915_gem_object *obj,
 update:
 	obj->tiling_changed = false;
 	switch (INTEL_INFO(dev)->gen) {
+	case 7:
 	case 6:
 		ret = sandybridge_write_fence_reg(obj, pipelined);
 		break;
@@ -2706,6 +2707,7 @@ i915_gem_clear_fence_reg(struct drm_device *dev,
 	uint32_t fence_reg = reg - dev_priv->fence_regs;
 
 	switch (INTEL_INFO(dev)->gen) {
+	case 7:
 	case 6:
 		I915_WRITE64(FENCE_REG_SANDYBRIDGE_0 + fence_reg*8, 0);
 		break;