board: STiH410-B2260: Set SYS_BOOTM_LEN to 16M

With recent kernel v4.18-rcx, uImage becomes bigger than 8MB.
Set SYS_BOOTM_LEN to 16MB, this fix the following error message:
"Fix Loading Kernel Image ... Image too large: increase
CONFIG_SYS_BOOTM_LEN"

Signed-off-by: Patrice Chotard <patrice.chotard@st.com>

include/configs/stih410-b2260.h

@@ -7,6 +7,8 @@
 #ifndef __CONFIG_H
 #define __CONFIG_H
 
+#include <linux/sizes.h>
+
 /* ram memory-related information */
 #define CONFIG_NR_DRAM_BANKS		1
 #define PHYS_SDRAM_1			0x40000000
@@ -19,6 +21,7 @@
 /* Environment */
 
 #define CONFIG_LOADADDR			CONFIG_SYS_LOAD_ADDR
+#define CONFIG_SYS_BOOTM_LEN		SZ_16M
 
 #define BOOT_TARGET_DEVICES(func) \
 	func(MMC, mmc, 0) \