serial: mxs-auart: support CMSPAR termios cflag

If CMSPAR is set in the c_cflag of termios, "stick" parity is enabled.

Tested on an i.MX28 system

Signed-off-by: Wolfgang Ocker <weo@reccoware.de>
Acked-by: Stefan Wahren <stefan.wahren@i2se.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>