staging: fsl-mc: Consolidate bus core header files

The DPAA2 objects involved (DPMNG, DPMCP, DPRC) are used by the fsl-mc
bus infrastructure only, so group the APIs and structs into
fsl-mc-private.h.

Signed-off-by: Bogdan Purcareata <bogdan.purcareata@nxp.com>
Reviewed-by: Laurentiu Tudor <laurentiu.tudor@nxp.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>