spi: spi-davinci: Add support for SPI_CS_WORD

This adds support for the SPI_CS_WORD flag to the TI DaVinci SPI
driver. This mode can be used as long as we are using the hardware
chip select and not a GPIO chip select.

Signed-off-by: David Lechner <david@lechnology.com>
Signed-off-by: Mark Brown <broonie@kernel.org>