mmc: dw_mmc: Add fifo watermark alignment property

Data done irq is expected if data length is less than
watermark in PIO mode. But fifo watermark is requested
to be aligned with data length in some SoC so that TX/RX
irq can be generated with data done irq. Add the
watermark alignment to mark this requirement and force
fifo watermark setting accordingly.

Signed-off-by: Jun Nie <jun.nie@linaro.org>
Reviewed-by: Shawn Lin <shawn.lin@rock-chips.com>
Signed-off-by: Jaehoon Chung <jh80.chung@samsung.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>