Add CBFS_TYPE_BOOTBLOCK to allow accessing the bootblock as a CBFS file. BUG=N/A TEST=build Change-Id: Ibb03ac3a6cd8711e0402e47335bb8e110c6ef61a Signed-off-by: Wim Vervoorn <wvervoorn@eltan.com> Reviewed-on: https://review.coreboot.org/c/coreboot/+/41824 Reviewed-by: Kyösti Mälkki <kyosti.malkki@gmail.com> Reviewed-by: Frans Hendriks <fhendriks@eltan.com> Tested-by: build bot (Jenkins) <no-reply@coreboot.org>