MX51: vision2: Fix build for vision2 board.

config.mk should not be used in board directory and should be removed.
Use the same approach for building the image as other MX51/MX53 boards.

After this change vision2 board can be built again.

Signed-off-by: Fabio Estevam <fabio.estevam@freescale.com>
diff --git a/boards.cfg b/boards.cfg
index c1ccd8b..5f7d69a 100644
--- a/boards.cfg
+++ b/boards.cfg
@@ -131,7 +131,7 @@
 mx53evk                      arm         armv7       mx53evk             freescale      mx5		mx53evk:IMX_CONFIG=board/freescale/mx53evk/imximage.cfg
 mx53loco                     arm         armv7       mx53loco            freescale      mx5		mx53loco:IMX_CONFIG=board/freescale/mx53loco/imximage.cfg
 mx53smd                      arm         armv7       mx53smd             freescale      mx5		mx53smd:IMX_CONFIG=board/freescale/mx53smd/imximage.cfg
-vision2                      arm         armv7       vision2             ttcontrol      mx5
+vision2                      arm         armv7       vision2             ttcontrol      mx5		vision2:IMX_CONFIG=board/ttcontrol/vision2/imximage_hynix.cfg
 cm_t35                       arm         armv7       cm_t35              -              omap3
 omap3_overo                  arm         armv7       overo               -              omap3
 omap3_pandora                arm         armv7       pandora             -              omap3