spi: mpc5xxx-psc: Remove unused platform_data

The platform_data for the MPC5xxx PSC SPI controllers is never used, so
remove it and the resulting code which depends on it.

Signed-off-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20230217-dt-mpc5xxx-spi-v1-1-3be8602fce1e@kernel.org


Signed-off-by: Mark Brown <broonie@kernel.org>