tty: serial: mpc5xxx: add support for mark/space parity

Tested on a custom MPC5200B-board using some fancy industrial protocol.
Verified that MPC512x has identical bits, so should work there as well.

Signed-off-by: Wolfram Sang <w.sang@pengutronix.de>
Acked-by: Anatolij Gustschin <agust@denx.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>