serial/mpc52xx_uart: add MPC5125 PSC support

Add MPC5125 PSC register layout structure, MPC5125 specific
psc_ops function set and the compatible string.

Signed-off-by: Vladimir Ermakov <vooon341@gmail.com>
Signed-off-by: Matteo Facchinetti <matteo.facchinetti@sirius-es.it>
Signed-off-by: Anatolij Gustschin <agust@denx.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>