spi: mpc512x-psc: add support for Freescale MPC5125

The register layout of the PSC devices differ between MPC5121 and
MPC5125, but the registers are named nearly identical and their purpose
is similar enough ("freescale identical") such that substituting
mpc52xx_psc by mpc5125_psc is nearly enough to make the driver work on
MPC5125. To keep supporting MPC5121 this patch introduces a cpp
macro to select the right struct that defines the register layout.

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Mark Brown <broonie@kernel.org>