drm/i915: Add support for changing LVDS panel fitting using an output property.

Previously the driver would always scale the chosen video mode to fill the
panel.  This adds 1:1 and maintain-aspect-ratio scaling modes.

v2: the drm_calloc/drm_free is replaced by kzalloc/kfree based
on Eric's suggestion.
Signed-off-by: Zhao Yakui <yakui.zhao@intel.com>
Signed-off-by: Eric Anholt <eric@anholt.net>

drivers/gpu/drm/i915/i915_reg.h

@@ -847,9 +847,25 @@
 #define   HORIZ_INTERP_MASK	(3 << 6)
 #define   HORIZ_AUTO_SCALE	(1 << 5)
 #define   PANEL_8TO6_DITHER_ENABLE (1 << 3)
+#define   PFIT_FILTER_FUZZY	(0 << 24)
+#define   PFIT_SCALING_AUTO	(0 << 26)
+#define   PFIT_SCALING_PROGRAMMED (1 << 26)
+#define   PFIT_SCALING_PILLAR	(2 << 26)
+#define   PFIT_SCALING_LETTER	(3 << 26)
 #define PFIT_PGM_RATIOS	0x61234
 #define   PFIT_VERT_SCALE_MASK			0xfff00000
 #define   PFIT_HORIZ_SCALE_MASK			0x0000fff0
+/* Pre-965 */
+#define		PFIT_VERT_SCALE_SHIFT		20
+#define		PFIT_VERT_SCALE_MASK		0xfff00000
+#define		PFIT_HORIZ_SCALE_SHIFT		4
+#define		PFIT_HORIZ_SCALE_MASK		0x0000fff0
+/* 965+ */
+#define		PFIT_VERT_SCALE_SHIFT_965	16
+#define		PFIT_VERT_SCALE_MASK_965	0x1fff0000
+#define		PFIT_HORIZ_SCALE_SHIFT_965	0
+#define		PFIT_HORIZ_SCALE_MASK_965	0x00001fff
+
 #define PFIT_AUTO_RATIOS 0x61238
 
 /* Backlight control */