env: split fw_env.h in public and private parts

Move U-Boot private data into a separate file. This
lets export fw_env.h to be used by external programs
that want to change the environment using the library
built in tools/env.

Signed-off-by: Stefano Babic <sbabic@denx.de>
diff --git a/tools/env/fw_env_main.c b/tools/env/fw_env_main.c
index 443de36..b8bff26 100644
--- a/tools/env/fw_env_main.c
+++ b/tools/env/fw_env_main.c
@@ -34,6 +34,7 @@
 #include <stdlib.h>
 #include <sys/file.h>
 #include <unistd.h>
+#include "fw_env_private.h"
 #include "fw_env.h"
 
 #define CMD_PRINTENV	"fw_printenv"