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/arch/arm64/boot.c

@@ -19,7 +19,6 @@
 #include <arch/transition.h>
 #include <arm_tf.h>
 #include <program_loading.h>
-#include <string.h>
 
 static void run_payload(struct prog *prog)
 {

src/arch/riscv/trap_handler.c

@@ -17,7 +17,6 @@
 #include <arch/encoding.h>
 #include <arch/exception.h>
 #include <console/console.h>
-#include <string.h>
 #include <vm.h>
 #include <mcall.h>
 #include <sbi.h>

src/arch/x86/boot.c

@@ -15,7 +15,6 @@
 #include <console/console.h>
 #include <program_loading.h>
 #include <ip_checksum.h>
-#include <string.h>
 #include <symbols.h>
 
 int payload_arch_usable_ram_quirk(uint64_t start, uint64_t size)