This patch adds QE buffer descriptors mode support for the
spi_mpc8xxx driver, and as a side effect we now support CPM1
and CPM2 SPI controllers.

That means that today we support almost all MPC SPI controllers:

- MPC834x-style controllers (support PIO mode only);
- CPM1 and CPM2 controllers (support DMA mode only);
- QE SPI controllers in CPU mode (PIO mode with shift quirks);
- QE SPI controllers in buffer descriptors (DMA) mode;

The only controller we don't currently support is a newer eSPI
(with a dedicated chip selects and a bit different registers map).
Signed-off-by: Anton Vorontsov <avorontsov@ru.mvista.com>
Acked-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>