drm: Add mode_config .get_format_info() hook

Allow drivers to return a custom drm_format_info structure for special
fb layouts. We'll use this for the compression control surface in i915.

v2: Fix drm_get_format_info() kernel doc (Laurent)
    Don't pass 'dev' to the new hook (Laurent)
v3: s/compresssion/compression/ (Ben)

Cc: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Cc: Ben Widawsky <ben@bwidawsk.net>
Cc: Jason Ekstrand <jason@jlekstrand.net>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Ben Widawsky <ben@bwidawsk.net>
Link: http://patchwork.freedesktop.org/patch/msgid/20170321181218.10042-4-ville.syrjala@linux.intel.com
diff --git a/include/drm/drm_fourcc.h b/include/drm/drm_fourcc.h
index fcc08da..6942e84 100644
--- a/include/drm/drm_fourcc.h
+++ b/include/drm/drm_fourcc.h
@@ -25,6 +25,9 @@
 #include <linux/types.h>
 #include <uapi/drm/drm_fourcc.h>
 
+struct drm_device;
+struct drm_mode_fb_cmd2;
+
 /**
  * struct drm_format_info - information about a DRM format
  * @format: 4CC format identifier (DRM_FORMAT_*)
@@ -55,6 +58,9 @@
 
 const struct drm_format_info *__drm_format_info(u32 format);
 const struct drm_format_info *drm_format_info(u32 format);
+const struct drm_format_info *
+drm_get_format_info(struct drm_device *dev,
+		    const struct drm_mode_fb_cmd2 *mode_cmd);
 uint32_t drm_mode_legacy_fb_format(uint32_t bpp, uint32_t depth);
 int drm_format_num_planes(uint32_t format);
 int drm_format_plane_cpp(uint32_t format, int plane);