set_gbb_flags: add '-p host' to flashrom command
set_gbb_flags: add '-p host' to flashrom command

BRANCH=none
BUG=chrome-os-partner:60894
TEST=set_gbb_flags 0

Change-Id: I22f372590bfe7705d4312588f971ad37f229a216
Reviewed-on: https://chromium-review.googlesource.com/418519
Commit-Ready: Ting Shen <c671d3efec3d7e7e285f3788bf0d1ba4c8605b78@chromium.org>
Tested-by: Ting Shen <c671d3efec3d7e7e285f3788bf0d1ba4c8605b78@chromium.org>
Reviewed-by: David Hendricks <3b0deacc4b5357f519084f1ea34bd42bf5d34545@chromium.org>

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