haswell boards: use libre mrc.bin replacement

courtesy of Angel Pons from the coreboot project

this uses the following patch set from gerrit, as yet
unmerged (in coreboot master) on this date:

    https://review.coreboot.org/c/coreboot/+/64198/5

logic for downloading mrc blobs has been deleted from
lbmk, as this is now completely obsolete (for haswell
boards)

if other platforms are added later that need mrc.bin,
then logic will be re-added again for that