[coreboot-gerrit] [L] Change in coreboot[master]: mainboard: Add SPDX license headers to Makefiles

[Yidi Lin (Code Review)]

Attention is currently required from: Alexander Couzens, Angel Pons, Damien Zammit, Elyes Haouas, Eran Mitrani, Evgeny Zinoviev, Hung-Te Lin, Jakub Czapiga, Jason Nien, Jeremy Soller, Kapil Porwal, Martin L Roth, Martin Roth, Matt DeVillier, Maxim Polyakov, Nico Huber, Subrata Banik, Tarun Tuli, Werner Zeh.

Yidi Lin has posted comments on this change. ( https://review.coreboot.org/c/coreboot/+/68982?usp=email )

Change subject: mainboard: Add SPDX license headers to Makefiles
......................................................................

Patch Set 3: Code-Review+2