To use SOURCE_DATE_EPOCH for the kernel build, extend genbuild_h to contain COREBOOT_BUILD_EPOCH. Change-Id: Iaa79d3e7df8101a1ba1b37a361d8992f7eab2d52 Signed-off-by: Alexander Couzens <lynxis@fe80.eu> Reviewed-on: https://review.coreboot.org/c/coreboot/+/51362 Tested-by: build bot (Jenkins) <no-reply@coreboot.org> Reviewed-by: Patrick Georgi <pgeorgi@google.com>