spi: mpc5xxx-psc: Use platform resources instead of parsing DT properties

The mpc52xx-psc and mpc512x-psc drivers use DT property parsing
functions for 'reg' and 'interrupts', but those are available as
platform device resources. Convert probe functions to use them and
simplify probe to a single function. For 'cell-index', also use the
preferred typed property function.

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


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