futility: Wipe GBB data before writing new values.
futility: Wipe GBB data before writing new values.

The previous version of gbb_utility always zeros data before
writing new values and we should keep this behavior, to simplify
firmware hash calculation and potential security concern.

BRANCH=none
BUG=chromium:413066
TEST=emerge gbb_utility; factory/bin/gooftool get_firmware_hash bios.bin
Original-Change-Id: Ic97a118cefc9698d52d9370b627670ff103d5e23

Change-Id: If38e15f35ee491cc80f96b360c63ee25f71c1854
Reviewed-on: https://chromium-review.googlesource.com/217700
Reviewed-by: Hung-Te Lin <8a7fce4940baad93a69f5073b383c85deed9d9c4@chromium.org>
Commit-Queue: Hung-Te Lin <8a7fce4940baad93a69f5073b383c85deed9d9c4@chromium.org>
Tested-by: Hung-Te Lin <8a7fce4940baad93a69f5073b383c85deed9d9c4@chromium.org>
(cherry picked from commit 3c8d29c204c6feb91ad951e2e1c5190d4ca98a13)
Reviewed-on: https://chromium-review.googlesource.com/217711
Commit-Queue: Bill Richardson <129945214b1d548d8e49b6c29c43094f8c78057f@chromium.org>
Tested-by: Bill Richardson <129945214b1d548d8e49b6c29c43094f8c78057f@chromium.org>
Reviewed-by: Randall Spangler <62698fdbb84d1779579ee80c3f39fac22017e5bc@chromium.org>

acorn-marvell/vboot_reference,geekboxzone/mmallow_external_vboot_reference,acorn-marvell/vboot_reference,acorn-marvell/vboot_reference,coreboot/vboot,geekboxzone/mmallow_external_vboot_reference,acorn-marvell/vboot_reference,coreboot/vboot,geekboxzone/mmallow_external_vboot_reference,coreboot/vboot,geekboxzone/mmallow_external_vboot_reference,coreboot/vboot,coreboot/vboot,geekboxzone/mmallow_external_vboot_reference