drm/i915: Add support for half float framebuffers on snb sprites

snb supports fp16 pixel formats on the sprite planes. Expose that
capability. Nothing special needs to be done, it just works.

v2: Rebase on top of icl fp16
    Split snb+ sprite bits into a separate patch
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/20191015193035.25982-11-ville.syrjala@linux.intel.com

drivers/gpu/drm/i915/display/intel_sprite.c

@@ -1653,6 +1653,12 @@ static u32 g4x_sprite_ctl(const struct intel_crtc_state *crtc_state,
 	case DRM_FORMAT_XRGB8888:
 		dvscntr |= DVS_FORMAT_RGBX888;
 		break;
+	case DRM_FORMAT_XBGR16161616F:
+		dvscntr |= DVS_FORMAT_RGBX161616 | DVS_RGB_ORDER_XBGR;
+		break;
+	case DRM_FORMAT_XRGB16161616F:
+		dvscntr |= DVS_FORMAT_RGBX161616;
+		break;
 	case DRM_FORMAT_YUYV:
 		dvscntr |= DVS_FORMAT_YUV422 | DVS_YUV_ORDER_YUYV;
 		break;
@@ -2367,8 +2373,10 @@ static const u64 i9xx_plane_format_modifiers[] = {
 };
 
 static const u32 snb_plane_formats[] = {
-	DRM_FORMAT_XBGR8888,
 	DRM_FORMAT_XRGB8888,
+	DRM_FORMAT_XBGR8888,
+	DRM_FORMAT_XRGB16161616F,
+	DRM_FORMAT_XBGR16161616F,
 	DRM_FORMAT_YUYV,
 	DRM_FORMAT_YVYU,
 	DRM_FORMAT_UYVY,