drm/i915: Shrink bxt_ddi_buf_trans

All the values we put into the BXT buf_trans tables fit into 8 bits.
So switch over to u8 from the u32 we use currently.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20170918182604.9519-3-ville.syrjala@linux.intel.com
Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>

drivers/gpu/drm/i915/intel_ddi.c

@@ -301,10 +301,10 @@ static const struct ddi_buf_trans skl_y_ddi_translations_hdmi[] = {
 };
 
 struct bxt_ddi_buf_trans {
-	u32 margin;	/* swing value */
-	u32 scale;	/* scale value */
-	u32 enable;	/* scale enable */
-	u32 deemphasis;
+	u8 margin;	/* swing value */
+	u8 scale;	/* scale value */
+	u8 enable;	/* scale enable */
+	u8 deemphasis;
 	bool default_index; /* true if the entry represents default value */
 };