spi: pxa2xx: Add support for Intel Elkhart Lake

Intel Elkhart Lake has the same LPSS than Intel Broxton. Add support for
it.

Signed-off-by: Jarkko Nikula <jarkko.nikula@linux.intel.com>
Link: https://lore.kernel.org/r/20190703114603.22301-1-jarkko.nikula@linux.intel.com


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