spi: davinci: use edma_write_slot() to setup EDMA PaRAM slot

Currently a series of EDMA API calls are being made to setup
various aspects of EDMA PaRAM slots for receive and transmit.

Instead setup the PaRAM using a local structure and write once
to the hardware using edma_write_slot()

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