xilinx_spi: Split into platform and of driver, support new IP, platform independence.

Hi,

To follow is a series of patches against the xilinx_spi driver.

The patchset is against 2.6.32-rc6

The patchset addresses several problems in the current driver:
* It's PPC only (OF and uses PPC specific memory operations)
* Only supporting big endian writes
* Supports only 8bit SPI, support for DS570 (also 16 or 32 bit) is added.
* A platform driver is introduced for non OF capable architectures.

These patches were posted as one big patch up to 4 iterations, not splitted into 4.

--Richard