drm/i915: Fix tiling pitch handling on 8xx.

The pitch field is an exponent on pre-965, so we were rejecting buffers
on 8xx that we shouldn't have.  915 got lucky in that the largest legal
value happened to match (8KB / 512 = 0x10), but 8xx has a smaller tile width.
Additionally, we programmed that bad value into the register on 8xx, so the
only pitch that would work correctly was 4096 (512-1023 pixels), while others
would probably give bad rendering or hangs.

Signed-off-by: Eric Anholt <eric@anholt.net>

fd.o bug #20473.
diff --git a/drivers/gpu/drm/i915/i915_reg.h b/drivers/gpu/drm/i915/i915_reg.h
index 9668cc0..375569d 100644
--- a/drivers/gpu/drm/i915/i915_reg.h
+++ b/drivers/gpu/drm/i915/i915_reg.h
@@ -190,7 +190,8 @@
 #define   I830_FENCE_SIZE_BITS(size)	((ffs((size) >> 19) - 1) << 8)
 #define   I830_FENCE_PITCH_SHIFT	4
 #define   I830_FENCE_REG_VALID		(1<<0)
-#define   I830_FENCE_MAX_PITCH_VAL	0x10
+#define   I915_FENCE_MAX_PITCH_VAL	0x10
+#define   I830_FENCE_MAX_PITCH_VAL	6
 #define   I830_FENCE_MAX_SIZE_VAL	(1<<8)
 
 #define   I915_FENCE_START_MASK		0x0ff00000