spi: xilinx: Make num_chipselect 8-bit in the struct xspi_platform_data

There is no use for whole 16-bit for the number of chip select pins.
Drop it to 8 bits and reshuffle the data structure layout to avoid
unnecessary paddings.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: Michal Simek <michal.simek@amd.com>
Link: https://msgid.link/r/20240308162920.46816-4-andriy.shevchenko@linux.intel.com


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