spi: davinci: Drop non-dm code

Now all boards which are using davinci SPI driver
have moved to SPL_DM so drop the unneeded non-dm code.

Cc: Adam Ford <aford173@gmail.com>
Signed-off-by: Jagan Teki <jagan@amarulasolutions.com>
Tested-by: Adam Ford <aford173@gmail.com> #da850-evm