staging: fsl-mc: rename mc-private.h to mc-bus.h

The definitions in mc-private.h are not strictly speaking
'private', they are bus-related definitions expected to be
referenced by bus driver components as well as system components
(gic, smmu, vfio).  Rename mc-private.h to mc-bus.h to more
accurately reflect expected use.

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