drm/i915: Add support for GPU soft reset on Ironlake.

Ironlake's graphics reset register has to be accessed via the MCHBAR,
rather than via PCI config space, which requires some refactoring.

Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
diff --git a/drivers/gpu/drm/i915/i915_reg.h b/drivers/gpu/drm/i915/i915_reg.h
index 565a7a3..b46e580 100644
--- a/drivers/gpu/drm/i915/i915_reg.h
+++ b/drivers/gpu/drm/i915/i915_reg.h
@@ -110,7 +110,8 @@
 #define LBB	0xf4
 
 /* Graphics reset regs */
-#define I965_GDRST 0xc0
+#define I965_GDRST 0xc0 /* PCI config register */
+#define ILK_GDSR 0x2ca4 /* MCHBAR offset */
 #define  GRDOM_FULL	(0<<2)
 #define  GRDOM_RENDER	(1<<2)
 #define  GRDOM_MEDIA	(3<<2)