net: stmmac: Honor DT parameter to force DMA store and forward mode

"snps,force_sf_dma_mode" is documented in stmmac device tree bindings,
but is never handled by the driver.
Signed-off-by: NChen-Yu Tsai <wens@csie.org>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/ethernet/stmicro/stmmac/stmmac_platform.c

@@ -56,6 +56,8 @@ static int stmmac_probe_config_dt(struct platform_device *pdev,
 					   sizeof(struct stmmac_mdio_bus_data),
 					   GFP_KERNEL);
 
+	plat->force_sf_dma_mode = of_property_read_bool(np, "snps,force_sf_dma_mode");
+
 	/*
 	 * Currently only the properties needed on SPEAr600
 	 * are provided. All other properties should be added