pico-imx6ul: Increase the CONFIG_ENV_OFFSET size

U-Boot binary has grown in such a way that it goes beyond the reserved
area for the environment variables.

Running "saveenv" causes U-Boot to hang because of this overlap.

Fix this problem by increasing the CONFIG_ENV_OFFSET size.

Also, in order to prevent this same problem in the future, use
CONFIG_BOARD_SIZE_LIMIT, which will detect the overlap in build-time.

CONFIG_BOARD_SIZE_LIMIT does not accept math expressions, so declare
CONFIG_ENV_OFFSET with its direct value instead.
Signed-off-by: NFabio Estevam <festevam@gmail.com>
Signed-off-by: NFabio Berton <fabio.berton@ossystems.com.br>
Signed-off-by: NOtavio Salvador <otavio@ossystems.com.br>

include/configs/pico-imx6ul.h

@@ -134,7 +134,19 @@
 
 /* environment organization */
 #define CONFIG_ENV_SIZE			SZ_8K
-#define CONFIG_ENV_OFFSET		(8 * SZ_64K)
+/* Environment starts at 768k = 768 * 1024 = 786432 */
+#define CONFIG_ENV_OFFSET		786432
+/*
+ * Detect overlap between U-Boot image and environment area in build-time
+ *
+ * CONFIG_BOARD_SIZE_LIMIT = CONFIG_ENV_OFFSET - u-boot.img offset
+ * CONFIG_BOARD_SIZE_LIMIT = 768k - 69k = 699k = 715776
+ *
+ * Currently CONFIG_BOARD_SIZE_LIMIT does not handle expressions, so
+ * write the direct value here
+ */
+#define CONFIG_BOARD_SIZE_LIMIT		715776
+
 
 #define CONFIG_SYS_MMC_ENV_DEV		0
 #define CONFIG_SYS_MMC_ENV_PART		0