Change IPMI chassis status to use xyz.openbmc_project.State.Chassis instead of pgood

[Bills, Jason M]

Hello,

In this review, I'm proposing that IPMI should not directly read the 
status of pgood for the IPMI Chassis Status and should instead use
xyz.openbmc_project.State.Chassis: 
https://gerrit.openbmc-project.xyz/c/openbmc/phosphor-host-ipmid/+/21787.

The change assumes that anyone using this IPMI command (and the current 
pgood property) also supports the xyz.openbmc_project.State.Chassis 
interface and the change will be seamless.  However, Emily wisely 
suggested in the review that I should double-check that assumption.

If there is anyone who requires the IPMI Chassis Status command to work 
using only pgood and not xyz.openbmc_project.State.Chassis, please 
comment in the review, so we can figure out the right solution.

Thanks!
-Jason