sbc8641d: increase malloc pool size to a sane default

Currently the board fails to save its env, since the env size
is much smaller than the sector size, and the malloc fails for
the pad buffer, giving the user visible symptom of:

Unable to save the rest of sector (253952)

Allow for 1M malloc pool, the same as used on the sbc8548 board.

Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>

include/configs/sbc8641d.h

@@ -242,7 +242,7 @@
 #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_MALLOC_LEN		(128 * 1024)    /* Reserved for malloc */
+#define CONFIG_SYS_MALLOC_LEN		(1024 * 1024)   /* Reserved for malloc */
 
 /* Serial Port */
 #define CONFIG_CONS_INDEX     1