spi: add spi controller v3 master driver for Blackfin

New spi controller(version 3) is integrated into Blackfin
60x processor. Comparing to bf5xx spi controller, we support
32 bits word size and independent receive and transmit DMA
channels now. Also mode 0 and 2 (CPHA = 0) can get fully
supported becasue cs line may be controlled by the software.

Signed-off-by: Scott Jiang <scott.jiang.linux@gmail.com>
Signed-off-by: Mark Brown <broonie@linaro.org>