spi: Add SPI master driver for DaVinci/DA8xx

This patch adds support for a SPI master driver for the
DaVinci series of SOCs

Signed-off-by: Sandeep Paulraj <s-paulraj@ti.com>
Signed-off-by: Mark A. Greer <mgreer@mvista.com>
Signed-off-by: Philby John <pjohn@in.mvista.com>
Signed-off-by: Sudhakar Rajashekhara <sudhakar.raj@ti.com>
Signed-off-by: Kevin Hilman <khilman@deeprootsystems.com>
Signed-off-by: Grant Likely <grant.likely@secretlab.ca>