Update Assembly Resource To Populate Status::State

[gtmills]

Similar to how we look at Operational Status to set the Status::Health Redfish property (See ibm-openbmc/bmcweb#202), we can look at the Present property on D-Bus to set the Status::State property

If Present is true, set Status::State to Enabled, else set it to Absent.

We do this for other resources like:
https://github.com/ibm-openbmc/bmcweb/blob/1020/redfish-core/lib/power_supply.hpp#L134

ibm-openbmc/bmcweb#247 is same issue

[SunnySrivastava1984]

Code updated under PR
ibm-openbmc/bmcweb#256

[mzipse]

Work is complete. Closing.