Relicense Makefile to match libpayload

Relicense Makefile to match libpayload

libpayload's license is more liberal than coreboot's. If we are to
use the coreboot build system for libpayload (bringing a couple of
new features to libpayload), we should adopt it for this shared part
even if not strictly necessary.

Change-Id: I1349616861e193b3e01407debbec3d82e09e72c2
Signed-off-by: Patrick Georgi <patrick@georgi-clan.de>
Reviewed-on: http://review.coreboot.org/70
Tested-by: build bot (Jenkins)
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>
Reviewed-by: Uwe Hermann <uwe@hermann-uwe.de>
Reviewed-by: Cristian Măgherușan-Stanciu <cristi.magherusan@gmail.com>