imx: mx6q/dl sabre_common: Move MMC ENV offset to 512KB position

Set the CONFIG_ENV_OFFSET from 384KB to 512KB offset, so we will have larger space
for u-boot image.
When enabling NAND flash support feature, the u-boot image size has exceeded the
384KB, which causes overlay to the environment variables storage.

Signed-off-by: Ye.Li <B37916@freescale.com>
Acked-by: Fabio Estevam <fabio.estevam@freescale.com>

include/configs/mx6sabre_common.h

@@ -251,7 +251,7 @@
 #define CONFIG_ENV_IS_IN_MMC
 
 #if defined(CONFIG_ENV_IS_IN_MMC)
-#define CONFIG_ENV_OFFSET		(6 * 64 * 1024)
+#define CONFIG_ENV_OFFSET		(8 * 64 * 1024)
 #endif
 
 #define CONFIG_OF_LIBFDT