Fix execution dependency with checkstop monitor

phosphor-gpio-monitor watching for checkstop instance is configured
to start at host-start target and to stop at host-stop target.

On detecting the checkstop condition, it is configured to invoke
obmc-host-crash target, which in turn would invoke host-quiesce
target.

Starting and stopping the gpio monitor was achieved by having 2
target files that had just 'Requires' relation with gpio-monitor.

This commit removes the target and uses '.wants' relationship and
puts a drop-in unit for establishing a `Conflicts` relation with
obmc-host-crash target, which is what is invoked by gpio-monitor
on detecting checkstop.

This will ensure that gpio-monitor is stopped before starting
crash target and not relying on power off to do the same.

Fixes openbmc/openbmc#2022

Change-Id: I4dee93859a533c4d1a5138f4c3dd048160301e03
Signed-off-by: Vishwanatha Subbanna <vishwa@linux.vnet.ibm.com>
4 files changed