Service files for factory reset change - clear instead of delete

This commit adds a new service file to the build which will clear the
contents of a specified UBI volume. It's intended as the backend for the
host factory reset.

Additionally, the service file obmc-flash-bios-ubiumount-prsv.service is
removed. This file removes the volume pnor-prsv. Its only use case - the
factory reset - is changing in this issue, openbmc/openbmc#2322, to
clear that volume instead of deleting it, so there's no reason to keep
the service file around anymore.

Change-Id: I577291e3511bf5234ffb87084a082255dac3dbae
Signed-off-by: Michael Tritz <mtritz@us.ibm.com>
4 files changed