staging: fsl-mc: clean up Kconfig description

Except for copyrights we are avoiding all references
to Freescale, which no longer exists as a brand.  Cleanup
Freescale references and simplify the Kconfig description
of the fsl-mc bus.

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