tools/env: Correct include kconfig

While we move some config macros to Kconfig, kconfig header is needed
to avoid compiling error if not already included.

Signed-off-by: York Sun <york.sun@nxp.com>
diff --git a/tools/envcrc.c b/tools/envcrc.c
index a9d9b48..e9fd088 100644
--- a/tools/envcrc.c
+++ b/tools/envcrc.c
@@ -12,6 +12,8 @@
 #include <string.h>
 #include <unistd.h>
 
+#include <linux/kconfig.h>
+
 #ifndef __ASSEMBLY__
 #define	__ASSEMBLY__			/* Dirty trick to get only #defines	*/
 #endif