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/BiosCallOuts.c

@@ -21,7 +21,6 @@
 #include <console/console.h>
 #include <soc/southbridge.h>
 #include <soc/pci_devs.h>
-#include <stdlib.h>
 #include <amdblocks/agesawrapper.h>
 #include <amdblocks/dimm_spd.h>
 #include <amdblocks/car.h>