Makefile: move determination test for the architecture to Makefile.d

Move the test code for architecture detection in a extra directory to
split it from the main flashrom code.

Change-Id: I29ce73be9c5cbe259a2471f8eea2f8745b68cdfa
Signed-off-by: Thomas Heijligen <thomas.heijligen@secunet.de>
Original-Reviewed-on: https://review.coreboot.org/c/flashrom/+/58269
Original-Reviewed-by: Nico Huber <nico.h@gmx.de>
Reviewed-on: https://review.coreboot.org/c/flashrom-stable/+/72242
Reviewed-by: Nico Huber <nico.h@gmx.de>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
4 files changed