scripts: Add the new GBB_FLAG_ENTER_TRIGGERS_TONORM usage
scripts: Add the new GBB_FLAG_ENTER_TRIGGERS_TONORM usage

This GBB_FLAG_ENTER_TRIGGERS_TONORM is new added for allowing Enter
(default is Space) to trigger the TONORM screen. This flag is
used by FAFT testing.

Chage the usage of set_gbb_flags.sh to help an user.

BUG=chrome-os-partner:12699
TEST=None. Trivial comment change.

Change-Id: I8a1efa880627965570719f22dedfa0e31ab2d5f5
Reviewed-on: https://gerrit.chromium.org/gerrit/33404
Reviewed-by: Hung-Te Lin <8a7fce4940baad93a69f5073b383c85deed9d9c4@chromium.org>
Commit-Ready: Tom Wai-Hong Tam <04b587fdf5845741a0c5a8b9cd59ca72d73ef8fc@chromium.org>
Tested-by: Tom Wai-Hong Tam <04b587fdf5845741a0c5a8b9cd59ca72d73ef8fc@chromium.org>
Reviewed-by: Randall Spangler <62698fdbb84d1779579ee80c3f39fac22017e5bc@chromium.org>

geekboxzone/mmallow_external_vboot_reference,marineam/seismograph,geekboxzone/mmallow_external_vboot_reference,coreboot/vboot,acorn-marvell/vboot_reference,geekboxzone/mmallow_external_vboot_reference,marineam/seismograph,coreboot/vboot,marineam/seismograph,coreboot/vboot,acorn-marvell/vboot_reference,ionave/seismograph,marineam/seismograph,ccaapton/vboot_reference,coreboot/vboot,acorn-marvell/vboot_reference,ionave/seismograph,ccaapton/vboot_reference,ionave/seismograph,geekboxzone/mmallow_external_vboot_reference,acorn-marvell/vboot_reference,ccaapton/vboot_reference,coreboot/vboot,ccaapton/vboot_reference,geekboxzone/mmallow_external_vboot_reference