mmc: dwmmc: socfpga: Get "fifo-mode" property from DT

Add FIFO mode support for SoCFPGA dwmmc, read "fifo-mode" property from DT.

Signed-off-by: Ley Foon Tan <ley.foon.tan@intel.com>
Reviewed-by: Jaehoon Chung <jh80.chung@samsung.com>