staging: fsl-mc: make fsl_mc_is_root_dprc() global

make fsl_mc_is_root_dprc() global so that the dprc driver
can use it

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