drm: move drm_mode_legacy_fb_format to drm_fourcc.c

It's part of the drm fourcc handling code, mapping the old depth/bpp
values to new fourcc codes.

Cc: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Archit Taneja <architt@codeaurora.org>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20160829082757.17913-6-daniel.vetter@ffwll.ch

include/drm/drm_crtc.h

@@ -2158,8 +2158,6 @@ extern int drm_mode_crtc_set_gamma_size(struct drm_crtc *crtc,
 
 extern int drm_mode_set_config_internal(struct drm_mode_set *set);
 
-extern uint32_t drm_mode_legacy_fb_format(uint32_t bpp, uint32_t depth);
-
 extern struct drm_tile_group *drm_mode_create_tile_group(struct drm_device *dev,
 							 char topology[8]);
 extern struct drm_tile_group *drm_mode_get_tile_group(struct drm_device *dev,

include/drm/drm_fourcc.h

@@ -25,6 +25,7 @@
 #include <linux/types.h>
 #include <uapi/drm/drm_fourcc.h>
 
+uint32_t drm_mode_legacy_fb_format(uint32_t bpp, uint32_t depth);
 void drm_fb_get_bpp_depth(uint32_t format, unsigned int *depth, int *bpp);
 int drm_format_num_planes(uint32_t format);
 int drm_format_plane_cpp(uint32_t format, int plane);