spi: davinci: remove 'wait_enable' platform data member
The SPI_READY bit of struct spi_device:mode serves the purpose
of letting the SPI master know if the slave can signal if it is
ready for transfer or not.
The 'wait_enable' platform data was duplicating this functionality.
Use the framework provided method of indicating this capability.
Signed-off-by: Brian Niebuhr <bniebuhr@efjohnson.com> Tested-By: Michael Williamson <michael.williamson@criticallink.com> Signed-off-by: Sekhar Nori <nsekhar@ti.com>