staging: fsl-mc: move mc-sys.h contents in the public header

mc-sys.h contains the API to send commands to the MC and is used
by drivers. Move it to the public headers and get rid of the mc-sys.h
header.

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