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/mediatek/common/ddp.c

@@ -15,7 +15,6 @@
 
 #include <device/mmio.h>
 #include <edid.h>
-#include <stdlib.h>
 #include <stddef.h>
 #include <soc/addressmap.h>
 #include <soc/ddp.h>

src/soc/mediatek/common/spi.c

@@ -18,7 +18,6 @@
 #include <console/console.h>
 #include <endian.h>
 #include <gpio.h>
-#include <stdlib.h>
 #include <soc/pll.h>
 #include <soc/spi.h>
 #include <timer.h>