powerpc/mpc8641hpcn: Move environment to avoid conflict

U-Boot on this board grew a long time ago past the 384 KiB that
it reserves for the U-Boot image, before the environment.  Thus,
saveenv overwrites the U-Boot image and bricks the board.

I tried to find out when U-Boot grew beyond this point, but there is a
long stretch in the history where this board did not build -- and
AFAICT when it did fit in 384 KiB, it was missing vital features such
as fdt support.  Turning off CONFIG_VIDEO was not enough to make it
fit.  Thus, I don't think we have any choice other than to move the
environment.

Signed-off-by: Scott Wood <scottwood@freescale.com>
Reviewed-by: York Sun <yorksun@freescale.com>

include/configs/MPC8641HPCN.h

@@ -255,7 +255,7 @@ extern unsigned long get_board_sys_clk(unsigned long dummy);
 #define CONFIG_SYS_GBL_DATA_OFFSET	(CONFIG_SYS_INIT_RAM_SIZE - GENERATED_GBL_DATA_SIZE)
 #define CONFIG_SYS_INIT_SP_OFFSET	CONFIG_SYS_GBL_DATA_OFFSET
 
-#define CONFIG_SYS_MONITOR_LEN		(256 * 1024)	/* Reserve 256 kB for Mon */
+#define CONFIG_SYS_MONITOR_LEN		(512 * 1024)	/* Reserve 512 kB for Mon */
 #define CONFIG_SYS_MALLOC_LEN		(1024 * 1024)	 /* Reserved for malloc */
 
 /* Serial Port */
@@ -602,7 +602,8 @@ extern unsigned long get_board_sys_clk(unsigned long dummy);
  */
 #ifndef CONFIG_SYS_RAMBOOT
     #define CONFIG_ENV_IS_IN_FLASH	1
-    #define CONFIG_ENV_ADDR		(CONFIG_SYS_MONITOR_BASE + 0x60000)
+    #define CONFIG_ENV_ADDR		\
+			(CONFIG_SYS_MONITOR_BASE + CONFIG_SYS_MONITOR_LEN)
     #define CONFIG_ENV_SECT_SIZE		0x10000	/* 64K(one sector) for env */
 #else
     #define CONFIG_ENV_IS_NOWHERE	1	/* Store ENV in memory only */