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/2048.c b/cmd/2048.c
index 42cd171..aa0f827 100644
--- a/cmd/2048.c
+++ b/cmd/2048.c
@@ -8,6 +8,7 @@
 #include <rand.h>
 #include <vsprintf.h>
 #include <linux/delay.h>
+#include <linux/string.h>
 
 #define SIZE 4
 static uint score;