global: Add <linux/string.h> instead of long indirect include path

In a number of cases we have C files which rely on a chain of indirect
include paths to get <linux/string.h> to be included via <command.h>. To
facilitate cleaning up <command.h> make this code directly include
<linux/string.h>.

Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/cmd/diag.c b/cmd/diag.c
index c6da5aa..4a88ab0 100644
--- a/cmd/diag.c
+++ b/cmd/diag.c
@@ -9,6 +9,7 @@
  */
 #include <command.h>
 #include <post.h>
+#include <linux/string.h>
 
 int do_diag(struct cmd_tbl *cmdtp, int flag, int argc, char *const argv[])
 {