spi: pxa2xx: Add support for both chip selects on Intel Braswell

Intel Braswell LPSS SPI controller actually has two chip selects and there
is no capabilities register where this could be found out. These two chip
selects are controlled by bits which are in slightly differrent location
than Broxton has.

Braswell Windows driver also starts chip select (ACPI DeviceSelection)
numbering from 1 so translate it to be suitable for Linux as well.

Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Reviewed-by: Jarkko Nikula <jarkko.nikula@linux.intel.com>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Signed-off-by: Mark Brown <broonie@kernel.org>