tree: Drop unused <string.h>

Change-Id: I0e216cbc4acf9571c65c345a1764e74485f89438
Signed-off-by: Elyes Haouas <ehaouas@noos.fr>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/81818
Reviewed-by: Yu-Ping Wu <yupingso@google.com>
Reviewed-by: Angel Pons <th3fanbus@gmail.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

src/drivers/sof/sof.c

@@ -4,7 +4,6 @@
 #include <acpi/acpigen.h>
 #include <device/device.h>
 #include <device/path.h>
-#include <string.h>
 
 #include "chip.h"