drm/i915/kbl: Add WaDisableDynamicCreditSharing

Bspec states that we need to turn off dynamic credit
sharing on kbl revid a0 and b0. This happens by writing bit 28
on 0x4ab8.

References: HSD#2225601, HSD#2226938, HSD#2225763
Signed-off-by: Mika Kuoppala <mika.kuoppala@intel.com>
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1465309159-30531-15-git-send-email-mika.kuoppala@intel.com
diff --git a/drivers/gpu/drm/i915/i915_reg.h b/drivers/gpu/drm/i915/i915_reg.h
index 4144fb7..56a54ea 100644
--- a/drivers/gpu/drm/i915/i915_reg.h
+++ b/drivers/gpu/drm/i915/i915_reg.h
@@ -1672,6 +1672,9 @@
 
 #define GEN7_TLB_RD_ADDR	_MMIO(0x4700)
 
+#define GAMT_CHKN_BIT_REG	_MMIO(0x4ab8)
+#define   GAMT_CHKN_DISABLE_DYNAMIC_CREDIT_SHARING	(1<<28)
+
 #if 0
 #define PRB0_TAIL	_MMIO(0x2030)
 #define PRB0_HEAD	_MMIO(0x2034)