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/timer.c b/cmd/timer.c
index 04fcd84..427309e 100644
--- a/cmd/timer.c
+++ b/cmd/timer.c
@@ -6,6 +6,7 @@
 
 #include <command.h>
 #include <time.h>
+#include <linux/string.h>
 
 static int do_timer(struct cmd_tbl *cmdtp, int flag, int argc,
 		    char *const argv[])