staging: fsl-mc: dprc: drop unused APIs

Leave only APIs that area actually used in the bus driver.
The patch is mostly mechanical, with a couple exceptions:
 - getters/setters were not removed even if only one of
   them is being used
 - versioning API was also left in place
They will be added back on an as-needed basis.

Signed-off-by: Laurentiu Tudor <laurentiu.tudor@nxp.com>
Acked-by: Stuart Yoder <stuart.yoder@nxp.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>