spi: davinci: Update configs to make it selectable on Keystone

Keystone2 SOCs share the SPI IP block with DaVinci based SOCs. Update
the config bits so that its usable on Keystone2 based SOCs.

Signed-off-by: Santosh Shilimkar <santosh.shilimkar@ti.com>
Signed-off-by: Mark Brown <broonie@linaro.org>