spi: pxa2xx: Allow number of chip select pins to be read from property

In some cases the number of the chip select pins might come from
the device property. Allow driver to use it.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Link: https://lore.kernel.org/r/20240417110334.2671228-2-andriy.shevchenko@linux.intel.com


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