TI DaVinci: Driver for the davinci SPI controller

This adds a driver for the SPI controller found on davinci
based SoCs from Texas Instruments.

Signed-off-by: Sekhar Nori <nsekhar@ti.com>
Signed-off-by: Sudhakar Rajashekhara <sudhakar.raj@ti.com>
Signed-off-by: Sandeep Paulraj <s-paulraj@ti.com>