spi: pxa2xx: Remove outdated documentation

The documentation is referring to the legacy enumeration of the SPI
host controllers and target devices. It has nothing to do with the
modern way, which is the only supported in kernel right now. Hence,
remove outdated documentation file.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Link: https://lore.kernel.org/r/20240417110334.2671228-5-andriy.shevchenko@linux.intel.com


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