spi: davinci: make chip-slect specific parameters really chip-select specific

Some chip-select specific paramterers like wdelay, parity, usage of
chip-select timers (and the actual timer values) are included in
platform data forcing the same behaviour across all chip-selects.

Create a new davinci_spi_config data structure which can be passed
along using controller_data member of spi_device data structure
on a per-device basis.

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