state: Add Available mapping for Power Supply

- Utilized resource util's getResourceState and getResourceHealth to
  get the Status.State and Status.Health of the power supply resource

Tested:
- Unit tests passed
- Redfish Service Validator passed
- Response as expected:
```
curl -k -v https://${bmc}/redfish/v1/Chassis/chassis/PowerSubsystem/PowerSupplies/powersupply0
```
Results in
```
{
  "@odata.id": "/redfish/v1/Chassis/chassis/PowerSubsystem/PowerSupplies/powersupply0",
  ...
  "SerialNumber": "Y YL106 63F0",
  "SparePartNumber": "0      ",
  "Status": {
    "Health": "OK",
    "State": "UnavailableOffline"
  }
  ...
}
```

Change-Id: I9fed94f7800fe01b6cb6de1a768da381bc116155
Signed-off-by: Justin Nguyen <justinnanguyen@gmail.com>