spi/pxa2xx: Restore private register bits.

The Intel LPSS SPI private register bits have to be restored
when system resume from S3 suspend.

Signed-off-by: Chew, Chiau Ee <chiau.ee.chew@intel.com>
Acked-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Signed-off-by: Mark Brown <broonie@linaro.org>