drm/i915: Clear PCODE_DATA1 on SNB+

Ville found out that the DATA1 register exists since SNB with some
scarce apparitions in the specs throughout the times. In his own words:

  Also according to Bspec the mailbox data1 register already existed
  since snb.  The hsw cdclk change sequence also mentions that it should
  be set to 0, but eg. the bdw IPS sequence doesn't mention it. I guess
  in theory some pcode command might cause it to be clobbered, so I'm
  thinking we should just explicitly set it to 0 for all platforms in
  the pcode read/write functions
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Suggested-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Damien Lespiau <damien.lespiau@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/i915_reg.h

@@ -6041,8 +6041,8 @@ enum punit_power_well {
 #define GEN6_PCODE_DATA				0x138128
 #define   GEN6_PCODE_FREQ_IA_RATIO_SHIFT	8
 #define   GEN6_PCODE_FREQ_RING_RATIO_SHIFT	16
+#define GEN6_PCODE_DATA1			0x13812C
 
-#define GEN9_PCODE_DATA1			0x13812C
 #define   GEN9_PCODE_READ_MEM_LATENCY		0x6
 #define   GEN9_MEM_LATENCY_LEVEL_MASK		0xFF
 #define   GEN9_MEM_LATENCY_LEVEL_1_5_SHIFT	8

drivers/gpu/drm/i915/intel_pm.c

@@ -7164,8 +7164,7 @@ int sandybridge_pcode_read(struct drm_i915_private *dev_priv, u8 mbox, u32 *val)
 	}
 
 	I915_WRITE(GEN6_PCODE_DATA, *val);
-	if (INTEL_INFO(dev_priv)->gen >= 9)
-		I915_WRITE(GEN9_PCODE_DATA1, 0);
+	I915_WRITE(GEN6_PCODE_DATA1, 0);
 	I915_WRITE(GEN6_PCODE_MAILBOX, GEN6_PCODE_READY | mbox);
 
 	if (wait_for((I915_READ(GEN6_PCODE_MAILBOX) & GEN6_PCODE_READY) == 0,