drm/i915: Expose the legacy LUT via the GAMMA_LUT/GAMMA_LUT_SIZE props on gen2/3

Just so we don't leave gen2/3 out in the cold let's advertize the
legacy LUT via the GAMMA_LUT/GAMMA_LUT_SIZE props. Without the
GAMMA_LUT prop we can't actually load a LUT using the atomic ioctl
(in preparation for the day of 100% atomic driver).

Supposedly some gen2/3 platforms have an interpolated 10bit gamma mode
as well. It's slightly funkier than the i965+ mode since you have to
specify the slope for the interpolation by hand. But when I tried it
I couldn't get it to work, the hardware just insisted on using the
8bit more regardless of the state of the relevant PIPECONF bit.

Reviewed-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190401200231.2333-7-ville.syrjala@linux.intel.com
Reviewed-by: Uma Shankar <uma.shankar@intel.com>

drivers/gpu/drm/i915/i915_pci.c

@@ -116,6 +116,8 @@
 		[PIPE_C] = IVB_CURSOR_C_OFFSET, \
 	}
 
+#define I9XX_COLORS \
+	.color = { .gamma_lut_size = 256 }
 #define I965_COLORS \
 	.color = { .gamma_lut_size = 129, \
 		   .gamma_lut_tests = DRM_COLOR_LUT_NON_DECREASING, \
@@ -156,6 +158,7 @@
 	.has_coherent_ggtt = false, \
 	I9XX_PIPE_OFFSETS, \
 	I9XX_CURSOR_OFFSETS, \
+	I9XX_COLORS, \
 	GEN_DEFAULT_PAGE_SIZES
 
 #define I845_FEATURES \
@@ -172,6 +175,7 @@
 	.has_coherent_ggtt = false, \
 	I845_PIPE_OFFSETS, \
 	I845_CURSOR_OFFSETS, \
+	I9XX_COLORS, \
 	GEN_DEFAULT_PAGE_SIZES
 
 static const struct intel_device_info intel_i830_info = {
@@ -205,6 +209,7 @@ static const struct intel_device_info intel_i865g_info = {
 	.has_coherent_ggtt = true, \
 	I9XX_PIPE_OFFSETS, \
 	I9XX_CURSOR_OFFSETS, \
+	I9XX_COLORS, \
 	GEN_DEFAULT_PAGE_SIZES
 
 static const struct intel_device_info intel_i915g_info = {