Makefile: move functions and macros to own file

Move all define statements in its own file to tidy up the main
Makefile.

Change-Id: I451f2eeab2773982e02b2f2fdc9e8abe1cc87630
Signed-off-by: Thomas Heijligen <thomas.heijligen@secunet.de>
Original-Reviewed-on: https://review.coreboot.org/c/flashrom/+/57935
Original-Reviewed-by: Nico Huber <nico.h@gmx.de>
Original-Reviewed-by: Angel Pons <th3fanbus@gmail.com>
Original-Reviewed-by:  Felix Singer <felixsinger@posteo.net>
Reviewed-on: https://review.coreboot.org/c/flashrom-stable/+/72236
Reviewed-by: Nico Huber <nico.h@gmx.de>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
2 files changed