staging: fsl-mc: decouple the mc-bus public headers from dprc.h

In its current form, the public headers of the mc-bus depend only on a
structure "dprc_obj_desc" defined in dprc.h. Move it to the bus public
header together with its associated defines and, in order to keep the
naming prefixes consistent rename it to "fsl_mc_obj_desc".
This will allow making dprc.h private in future patches.

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