Enhance vbutil_what_keys to work on BIOS images too.
Enhance vbutil_what_keys to work on BIOS images too.

BUG=none
TEST=none

Change-Id: I3bc15e18dcb9f89346815615be48729b8966736c
Reviewed-on: https://gerrit.chromium.org/gerrit/13014
Tested-by: Bill Richardson <129945214b1d548d8e49b6c29c43094f8c78057f@chromium.org>
Reviewed-by: Randall Spangler <62698fdbb84d1779579ee80c3f39fac22017e5bc@chromium.org>

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