haswell: only provide NRI-based ROMs in releases
    
    release="n" is set in target.cfg on haswell build targets
    that use mrc.bin
    
    script/update/release exports LBMK_RELEASE="y"
    
    script/build/roms skips building a given target if release="n"
    in target.cfg *and* LBMK_RELEASE="y"
    
    you could also do the export yourself before running ./build roms,
    for example:
    
    export LBMK_RELEASE="y"
    ./build roms all
    
    This would skip these ROM images. The native haswell raminit is
    now stable enough in my testing, that I wish to delete the MRC-based
    targets. This is in line with Libreboot's Binary Blob Reduction Policy,
    which states: if a blob can be avoided, it should be avoided.
    
    The problem is that users often run the inject script in *lbmk* from
    Git, instead of from the src release archive. I forsee some users
    running this on modern lbmk with older release images. If the mrc-based
    target isn't there, the user may use an NRI-based target name, and
    think it works; they will insert without MRC. I foresaw this ages
    ago, which is why Caleb and I ensured that the script checks hashes,
    and hashes are included in releases.
    
    Therefore: for the time being, keep the MRC-based configs in lbmk
    but do not include images for them in releases. This can be done
    indefinitely, but I'll probably remove those configs entirely at
    some point.
    
    On the following boards, Libreboot now will *only* provide NRI-based
    ROM images for the following machines:
    
    * Dell OptiPlex 9020 SFF
    * Dell OptiPlex 9020 MT
    * Lenovo ThinkPad T440p
    * Lenovo ThinkPad W541/W540
    
    I now recommend exclusive use of NRI-based images, on Haswell
    hardware. It's stable enough in my testing, and now supports S3.
    
    Signed-off-by: Leah Rowe <leah@libreboot.org>