OPAL_PCI_GET_POWER_STATE
========================

Get PCI slot power state

Parameter
---------

``uint64_t id``
  PCI slot ID

``uint64_t data``
  memory buffer pointer for power state

Calling
-------

Retrieve PCI slot's power state. The retrieved power state is stored
in buffer pointed by @data.

Return Codes
------------
OPAL_SUCCESS
  PCI slot's power state is retrieved successfully

OPAL_PARAMETER
  The indicated PCI slot isn't found

OPAL_UNSUPPORTED
  Power state retrieval not supported on the PCI slot