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>
---
Cc: Andrew Davis <afd@ti.com>
Cc: Bin Meng <bmeng.cn@gmail.com>
Cc: Dai Okamura <okamura.dai@socionext.com>
Cc: Fabio Estevam <festevam@gmail.com>
Cc: Francesco Dolcini <francesco.dolcini@toradex.com>
Cc: Ilias Apalodimas <ilias.apalodimas@linaro.org>
Cc: Jens Wiklander <jens.wiklander@linaro.org>
Cc: Kunihiko Hayashi <hayashi.kunihiko@socionext.com>
Cc: Mingkai Hu <mingkai.hu@nxp.com>
Cc: Priyanka Jain <priyanka.jain@nxp.com>
Cc: Shengzhou Liu <Shengzhou.Liu@nxp.com>
Cc: Simon Glass <sjg@chromium.org>
Cc: Stefano Babic <sbabic@nabladev.com>
Cc: Svyatoslav Ryhel <clamor95@gmail.com>
Cc: Thierry Reding <treding@nvidia.com>
Cc: William Zhang <william.zhang@broadcom.com>

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[])