drm/i915: Deobfuscate the render p-state obfuscation

The ironlake render p-state support includes some rather odd variable
names. Clean them up in order to improve the readability of the code.

Signed-off-by: Matthew Garrett <mjg@redhat.com>
Signed-off-by: Eric Anholt <eric@anholt.net>
diff --git a/drivers/gpu/drm/i915/i915_reg.h b/drivers/gpu/drm/i915/i915_reg.h
index c3948ee..d344c03 100644
--- a/drivers/gpu/drm/i915/i915_reg.h
+++ b/drivers/gpu/drm/i915/i915_reg.h
@@ -907,7 +907,7 @@
 #define RCBMINAVG		0x111a0
 #define RCUPEI			0x111b0
 #define RCDNEI			0x111b4
-#define RSTDBYCTL		0x111b8
+#define MCHBAR_RENDER_STANDBY		0x111b8
 #define   RCX_SW_EXIT		(1<<23)
 #define   RSX_STATUS_MASK	0x00700000
 #define VIDCTL			0x111c0