staging: fsl-mc: Remove remaining files

Remove the staging/drivers/fsl-mc directory from the staging
area now that all the components have been moved to the main
kernel areas.

Signed-off-by: Roy Pledge <roy.pledge@nxp.com>
Reviewed-by: Horia Geantă <horia.geanta@nxp.com>
Reviewed-by: Ioana Radulescu <ruxandra.radulescu@nxp.com>
Signed-off-by: Li Yang <leoyang.li@nxp.com>