ADS5121 DIU Make inclusion of FSL logo optional

Make inclusion of FSL logo optional and
turn it off by default.

Signed-off-by: John Rigby <jrigby@freescale.com>
diff --git a/board/ads5121/ads5121_diu.c b/board/ads5121/ads5121_diu.c
index 4f7dda0..565b63d 100644
--- a/board/ads5121/ads5121_diu.c
+++ b/board/ads5121/ads5121_diu.c
@@ -37,7 +37,11 @@
 #include <video_fb.h>
 #endif
 
+#ifdef CONFIG_FSL_DIU_LOGO_BMP
 extern unsigned int FSL_Logo_BMP[];
+#else
+#define FSL_Logo_BMP NULL
+#endif
 
 static int xres, yres;