soc/{amd,cavium,mediatek,sifive}: Remove unused <stdlib.h>

Change-Id: I83322e246fe81b97188be17a3fdda16d36df0678
Signed-off-by: Elyes HAOUAS <ehaouas@noos.fr>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/33688
Reviewed-by: Kyösti Mälkki <kyosti.malkki@gmail.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

src/soc/amd/stoneyridge/northbridge.c

@@ -36,7 +36,6 @@
 #include <soc/pci_devs.h>
 #include <soc/iomap.h>
 #include <stdint.h>
-#include <stdlib.h>
 #include <string.h>
 #include <arch/bert_storage.h>