drm/i915/skl: Buffer translation improvements

This patch adds support for 0.85V VccIO on Skylake Y,
separate buffer translation tables for Skylake U,
and support for I_boost for the entries that needs this.

Changes in v2:
* Refactored the code a bit to move all DDI signal level setup to
  intel_ddi.c

Issue: VIZ-5677
Signed-off-by: David Weinehall <david.weinehall@linux.intel.com>
Reviewed-by: Antti Koskipää <antti.koskipaa@linux.intel.com>
[danvet: Apply style polish checkpatch suggested.]
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index 6acc650..64041e7 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -2436,6 +2436,14 @@
 /* ULX machines are also considered ULT. */
 #define IS_HSW_ULX(dev)		(INTEL_DEVID(dev) == 0x0A0E || \
 				 INTEL_DEVID(dev) == 0x0A1E)
+#define IS_SKL_ULT(dev)		(INTEL_DEVID(dev) == 0x1906 || \
+				 INTEL_DEVID(dev) == 0x1913 || \
+				 INTEL_DEVID(dev) == 0x1916 || \
+				 INTEL_DEVID(dev) == 0x1921 || \
+				 INTEL_DEVID(dev) == 0x1926)
+#define IS_SKL_ULX(dev)		(INTEL_DEVID(dev) == 0x190E || \
+				 INTEL_DEVID(dev) == 0x1915 || \
+				 INTEL_DEVID(dev) == 0x191E)
 #define IS_PRELIMINARY_HW(intel_info) ((intel_info)->is_preliminary)
 
 #define SKL_REVID_A0		(0x0)