spi: pxa2xx: Switch to use BIT() and GENMASK() in pxa2xx_ssp.h

Switch pxa2xx_ssp.h header to use BIT() and GENMASK().
It's better to read and understand. While here, correct ordering
of some definitions.
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://lore.kernel.org/r/20200826151455.55970-2-andriy.shevchenko@linux.intel.comSigned-off-by: Mark Brown <broonie@kernel.org>