spi: davinci: removed unused #defines

Remove unused defines from code which should help
in easy reading of code.

Also, use the opportuinity to keep the SPIGCR1
register defines together.

Tested-By: Michael Williamson <michael.williamson@criticallink.com>
Tested-By: Brian Niebuhr <bniebuhr@efjohnson.com>
Signed-off-by: Sekhar Nori <nsekhar@ti.com>