mx7_common: Define CONFIG_SYS_MALLOC_LEN in the board file

Having CONFIG_SYS_MALLOC_LEN in mx7_common.h is not a good idea,
because the malloc() pool size is board dependent.

For example: if a certain board has support for splashscreen or DFU,
it may be necessary to adjust CONFIG_SYS_MALLOC_LEN to a larger value.

So define CONFIG_SYS_MALLOC_LEN in each board config file.

Signed-off-by: Fabio Estevam <fabio.estevam@nxp.com>
diff --git a/include/configs/mx7dsabresd.h b/include/configs/mx7dsabresd.h
index 988d363..25ed29d 100644
--- a/include/configs/mx7dsabresd.h
+++ b/include/configs/mx7dsabresd.h
@@ -16,6 +16,9 @@
 
 #define CONFIG_MXC_UART_BASE            UART1_IPS_BASE_ADDR
 
+/* Size of malloc() pool */
+#define CONFIG_SYS_MALLOC_LEN		(32 * SZ_1M)
+
 #define CONFIG_BOARD_EARLY_INIT_F
 #define CONFIG_BOARD_LATE_INIT