spi/pxa2xx-pci: Add PCI mode support for BayTrail LPSS SPI

Similar to CE4100, BayTrail LPSS SPI can be PCI enumerated
as well. Thus, the functions are renamed from ce4100_xxx
to pxa2xx_spi_pci_xxx to clarify that this is a generic
PCI glue layer. Also, added required infrastructure to
support SPI hosts with different configurations.

This patch is based on Mika Westerberg's previous work.

Signed-off-by: Chew, Chiau Ee <chiau.ee.chew@intel.com>
Signed-off-by: Mark Brown <broonie@linaro.org>