scripts: Change anti-rollback check from error to warning for make_dev_firmware.
scripts: Change anti-rollback check from error to warning for make_dev_firmware.

Currently make_dev_firmware will abort if the stored TPM version is
higher and ask user to reset TPM; however that is not very feasible
because:

(1) If the device is still MP-signed, external users can't boot
    dev-signed factory shim or recovery or test images.
(2) Even if the user is able to reset TPM, the stored TPM version
    will be increased again when user boots into the image for
    running make_dev_firmware.

As a result, the right flow is to allow user (with warning and
instructions) resign firmware with dev-keys, boot into recovery mode due
to anti-rollback check, and then boot any dev-signed image to reset TPM.

BRANCH=none
BUG=None
TEST=./make_dev_firmware.sh # see warning message.

Change-Id: Ifd4cd9912ab505427c985154b3f469e1485789b2
Reviewed-on: https://chromium-review.googlesource.com/419898
Commit-Ready: Hung-Te Lin <8a7fce4940baad93a69f5073b383c85deed9d9c4@chromium.org>
Tested-by: Hung-Te Lin <8a7fce4940baad93a69f5073b383c85deed9d9c4@chromium.org>
Reviewed-by: Mattias Nissler <f2124f8e21694335a48d099eb9510c5c4dda0d0b@chromium.org>
Reviewed-by: Bill Richardson <129945214b1d548d8e49b6c29c43094f8c78057f@chromium.org>

coreboot/vboot,coreboot/vboot,coreboot/vboot,coreboot/vboot,coreboot/vboot