Makefile: use HAS_ USE_ pattern for serial support

Align the usage of serial function with the selection of other
dependencies.

Change-Id: Ica951e76d6362b01f09d23a729a2a6049e7f0b66
Signed-off-by: Thomas Heijligen <thomas.heijligen@secunet.com>
Original-Reviewed-on: https://review.coreboot.org/c/flashrom/+/62196
Original-Reviewed-by: Nico Huber <nico.h@gmx.de>
Reviewed-on: https://review.coreboot.org/c/flashrom-stable/+/72307
Reviewed-by: Nico Huber <nico.h@gmx.de>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
1 file changed