spi: pxa2xx: Default thresholds to PXA configuration

Most of the devices in the supported list have PXA configuration of FIFO. In
particularly Intel Medfield and Merrifield have bigger FIFO, than it's defined
for CE4100.

Split CE4100 in the similar way how it was done for Intel Quark, i.e. prefix
definitions by CE4100 and append necessary pieces of code to switch case
conditions.

We are on safe side since those bits are ignored on all LPSS IPs.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: Jarkko Nikula <jarkko.nikula@linux.intel.com>
Signed-off-by: Mark Brown <broonie@kernel.org>