drm/i915: Enable YUV to RGB for Gen10 in Plane Ctrl Reg

If the fb format is YUV, enable the plane CSC mode bits
for the conversion.

v2: Addressed review comments from Shashank Sharma
Alignment issue fixed in i915_reg.h

v3: Adding Reviewed By from Shashank Sharma

v4: Rebased the patch. As part of rebasing, re-using
the color series defines which are already merged.
plane_state->base.color_encoding might not be set for
NV12. For now, just using PLANE_COLOR_CSC_MODE_YUV709_TO_RGB709
in glk_plane_color_ctl if format is NV12.

v5: Added reviewed by from Juha-Pekka Heikkila

v6: Rebased the series
Reviewed-by: NShashank Sharma <shashank.sharma@intel.com>
Reviewed-by: NJuha-Pekka Heikkila <juhapekka.heikkila@gmail.com>
Signed-off-by: NVidya Srinivas <vidya.srinivas@intel.com>
Reviewed-by: NMaarten Lankhorst <maarten.lankhorst@linux.intel.com>
Signed-off-by: NMaarten Lankhorst <maarten.lankhorst@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/1523245273-30264-12-git-send-email-vidya.srinivas@intel.com

drivers/gpu/drm/i915/intel_display.c

@@ -3630,6 +3630,11 @@ u32 glk_plane_color_ctl(const struct intel_crtc_state *crtc_state,
 	plane_color_ctl |= glk_plane_color_ctl_alpha(fb->format->format);
 
 	if (intel_format_is_yuv(fb->format->format)) {
+		if (fb->format->format == DRM_FORMAT_NV12) {
+			plane_color_ctl |=
+				PLANE_COLOR_CSC_MODE_YUV709_TO_RGB709;
+			goto out;
+		}
 		if (plane_state->base.color_encoding == DRM_COLOR_YCBCR_BT709)
 			plane_color_ctl |= PLANE_COLOR_CSC_MODE_YUV709_TO_RGB709;
 		else
@@ -3638,7 +3643,7 @@ u32 glk_plane_color_ctl(const struct intel_crtc_state *crtc_state,
 		if (plane_state->base.color_range == DRM_COLOR_YCBCR_FULL_RANGE)
 			plane_color_ctl |= PLANE_COLOR_YUV_RANGE_CORRECTION_DISABLE;
 	}
-
+out:
 	return plane_color_ctl;
 }