spi: rockchip: remove unneeded dma_caps

We no longer need the dma_caps since the dma driver
already clamps the burst length to the hardware limit,
so don't request and store dma_caps in device data.

Signed-off-by: Emil Renner Berthing <kernel@esmil.dk>
Signed-off-by: Mark Brown <broonie@kernel.org>