tools: fix fw_printenv tool to compile again

This patch updates the fw_printenv/fw_setenv userspace tool to include
the correct MTD header in order to compile against current kernel
headers. Backward compatibility is preserved by introducing an option
MTD_VERSION which can be set to "old" for compilation using the old MTD
headers. Along with this a number of warnings are fixed.

Signed-off-by: Markus Klotzbuecher <mk@denx.de>
diff --git a/tools/env/fw_env.h b/tools/env/fw_env.h
index 13c45a2..58607de 100644
--- a/tools/env/fw_env.h
+++ b/tools/env/fw_env.h
@@ -47,8 +47,8 @@
 	"ip=${ipaddr}:${serverip}:${gatewayip}:${netmask}:${hostname}::off; " 	\
 	"bootm"
 
-extern		void  fw_printenv(int argc, char *argv[]);
-extern unsigned char *fw_getenv  (unsigned char *name);
-extern		int   fw_setenv  (int argc, char *argv[]);
+extern void  fw_printenv(int argc, char *argv[]);
+extern char *fw_getenv  (char *name);
+extern int fw_setenv  (int argc, char *argv[]);
 
 extern unsigned	long  crc32	 (unsigned long, const unsigned char *, unsigned);