Instead of forcing the hardcoded 'devicetree.cb' filename under the mainboard directory, this allows mainboards to select a filename for the devicetree file. This allows mainboard variants that need to use different devicetree files to live under the same directory. Change-Id: I761e676ba5d5f70d1fb86656b528f63db169fcef Signed-off-by: Martin Roth <martinroth@google.com> Reviewed-on: https://review.coreboot.org/12529 Tested-by: build bot (Jenkins) Reviewed-by: Patrick Georgi <pgeorgi@google.com>