Increase max gunzip size in mvebu_armada-37xx.h.
This is required in order to boot itb images.

--- a/include/configs/mvebu_armada-37xx.h
+++ b/include/configs/mvebu_armada-37xx.h
@@ -12,6 +12,7 @@
 
 /* additions for new ARM relocation support */
 #define CONFIG_SYS_SDRAM_BASE	0x00000000
+#define CONFIG_SYS_BOOTM_LEN   (64 << 20)      /* Increase max gunzip size */
 
 #define CONFIG_NR_DRAM_BANKS	1