src/northbridge: Remove unused <stdlib.h>

Change-Id: I7a214196b05d3af06c8cd742a6154b0627a0d82f
Signed-off-by: Elyes HAOUAS <ehaouas@noos.fr>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/33685
Reviewed-by: Kyösti Mälkki <kyosti.malkki@gmail.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

src/northbridge/intel/haswell/gma.c

@@ -29,7 +29,6 @@
 #include <cpu/intel/haswell/haswell.h>
 #include <drivers/intel/gma/opregion.h>
 #include <southbridge/intel/lynxpoint/nvs.h>
-#include <stdlib.h>
 #include <string.h>
 #include <types.h>