src: Use 'include <string.h>' when appropriate

Drop 'include <string.h>' when it is not used and
add it when it is missing.
Also extra lines removed, or added just before local includes.

Change-Id: Iccac4dbaa2dd4144fc347af36ecfc9747da3de20
Signed-off-by: Elyes HAOUAS <ehaouas@noos.fr>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/31966
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Werner Zeh <werner.zeh@siemens.com>
Reviewed-by: Kyösti Mälkki <kyosti.malkki@gmail.com>

src/soc/intel/apollolake/romstage.c

@@ -48,7 +48,6 @@
 #include <soc/romstage.h>
 #include <soc/systemagent.h>
 #include <spi_flash.h>
-#include <string.h>
 #include <timer.h>
 #include <timestamp.h>
 #include "chip.h"

src/soc/intel/apollolake/uart.c

@@ -24,7 +24,6 @@
 #include <intelblocks/uart.h>
 #include <soc/gpio.h>
 #include <soc/pci_devs.h>
-#include <string.h>
 
 /* UART pad configuration. Support RXD and TXD for now. */
 const struct uart_gpio_pad_config uart_gpio_pads[] = {