i2c: at91: remove legacy DMA left overs

Commit dc6df6e9 ("i2c: at91: remove legacy DMA support") removed legcy
DMA support from the driver. Remove the last use of the definitions from
linux/platform_data/dma-atmel.h and stop including this header.

Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Reviewed-by: Codrin Ciubotariu <codrin.ciubotariu@microchip.com>
[wsa: fixed typo in subject]
Signed-off-by: Wolfram Sang <wsa@kernel.org>