dmaengine: ste_dma40: indicate granularity on channels

The ste_dma40 has burst level granularity on the residue
registers, which is necessary for some  clients to know,
notably the UART. Before this patch we get this message:

uart-pl011 80007000.uart: RX DMA disabled - no residue processing

This patch fixes it.

Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>