binman: add sign option for binman

Introduce proof of concept for binman's new option which provides sign
and replace FIT containers in binary images.

Usage as example:

from:
mkimage -G privateky -r -o sha256,rsa4096 -F fit
binman replace -i flash.bin -f fit.fit fit

to:
binman sign -i flash.bin -k privatekey -a sha256,rsa4096 -f fit.fit fit

and to this one if it's need to be extracted, signed with key and put it
back in image:
binman sign -i flash.bin -k privatekey -a sha256,rsa4096 fit

Signed-off-by: Ivan Mikhaylov <fr0st61te@gmail.com>
diff --git a/common/main.c b/common/main.c
index 682f335..7c70de2 100644
--- a/common/main.c
+++ b/common/main.c
@@ -13,6 +13,7 @@
 #include <command.h>
 #include <console.h>
 #include <env.h>
+#include <fdtdec.h>
 #include <init.h>
 #include <net.h>
 #include <version_string.h>