mx6sabre_common: Fix U-Boot corruption after 'saveenv'

Booting mx6qp sabreauto board and then doing:

=> saveenv
=> reset

, causes a system hang.

This happens because the size of the U-Boot binary is larger than
CONFIG_ENV_OFFSET.

Fix this problem by increasing CONFIG_ENV_OFFSET, so that the U-boot binary
and the environment variables region do not overlap.

Signed-off-by: Fabio Estevam <fabio.estevam@nxp.com>

include/configs/mx6sabre_common.h

@@ -209,7 +209,7 @@
 #define CONFIG_ENV_IS_IN_MMC
 
 #if defined(CONFIG_ENV_IS_IN_MMC)
-#define CONFIG_ENV_OFFSET		(8 * 64 * 1024)
+#define CONFIG_ENV_OFFSET		(768 * 1024)
 #endif
 
 /* Framebuffer */