drm: Clean up the 1366x768 fixup codes

This is just a cleanup, no functional change.

The fixup code for 1366x768 in drm_mode_create_from_cmdline_mode() is
basically a copy of the existing code in drm_edid.c.  Make the latter
code public so that it can be called from the former function.

Signed-off-by: Takashi Iwai <tiwai@suse.de>
Link: http://patchwork.freedesktop.org/patch/msgid/20170117164329.10551-1-tiwai@suse.de
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
[vsyrjala: include drm_crtc_internal.h to make sparse happy]
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
diff --git a/drivers/gpu/drm/drm_modes.c b/drivers/gpu/drm/drm_modes.c
index a8616b1..fd22c1c 100644
--- a/drivers/gpu/drm/drm_modes.c
+++ b/drivers/gpu/drm/drm_modes.c
@@ -1481,12 +1481,8 @@ drm_mode_create_from_cmdline_mode(struct drm_device *dev,
 
 	mode->type |= DRM_MODE_TYPE_USERDEF;
 	/* fix up 1368x768: GFT/CVT can't express 1366 width due to alignment */
-	if (cmd->xres == 1366 && mode->hdisplay == 1368) {
-		mode->hdisplay = 1366;
-		mode->hsync_start--;
-		mode->hsync_end--;
-		drm_mode_set_name(mode);
-	}
+	if (cmd->xres == 1366)
+		drm_mode_fixup_1366x768(mode);
 	drm_mode_set_crtcinfo(mode, CRTC_INTERLACE_HALVE_V);
 	return mode;
 }