staging: fsl-mc: move rest of mc-bus.h to private header

All the mc-bus.h contents is only used privately in the bus driver so
move everything to the private header and get rid of the mc-bus.h
header file.

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