mmc: sdhci-esdhc-imx: enable SDR50 tuning for imx6q/dl

The imx6q/dl supports SDR50 tunning, enable it for a better timing
on SDR50 mode.
Signed-off-by: NDong Aisheng <b29396@freescale.com>
Acked-by: NShawn Guo <shawn.guo@linaro.org>
Signed-off-by: NChris Ball <cjb@laptop.org>

drivers/mmc/host/sdhci-esdhc-imx.c

@@ -257,7 +257,8 @@ static u32 esdhc_readl_le(struct sdhci_host *host, int reg)
 			else
 				/* imx6q/dl does not have cap_1 register, fake one */
 				val = SDHCI_SUPPORT_DDR50 | SDHCI_SUPPORT_SDR104
-					| SDHCI_SUPPORT_SDR50;
+					| SDHCI_SUPPORT_SDR50
+					| SDHCI_USE_SDR50_TUNING;
 		}
 	}