mmc: mmci: Add DT bindings for feedback clock pin

The ST Micro variant supports the option of using a feedback clock signal in
favor of the clockout pin when latching incoming signals on the data bus.

Since this is matter of how pins are being routed we need to provide a new DT
binding to be able to configure this through DT.
Signed-off-by: NUlf Hansson <ulf.hansson@linaro.org>
Reviewed-by: NLinus Walleij <linus.walleij@linaro.org>

Documentation/devicetree/bindings/mmc/mmci.txt

@@ -24,6 +24,7 @@ Optional properties:
 - st,sig-dir-dat31       : bus signal direction pin used for DAT[3] and DAT[1].
 - st,sig-dir-dat74       : bus signal direction pin used for DAT[4] to DAT[7].
 - st,sig-dir-cmd         : cmd signal direction pin used for CMD.
+- st,sig-pin-fbclk       : feedback clock signal pin used.
 
 Example:
 
@@ -47,6 +48,7 @@ sdi0_per1@80126000 {
 	st,sig-dir-dat0;
 	st,sig-dir-dat2;
 	st,sig-dir-cmd;
+	st,sig-pin-fbclk;
 
 	vmmc-supply = <&ab8500_ldo_aux3_reg>;
 	vqmmc-supply = <&vmmci>;

drivers/mmc/host/mmci.c

@@ -1402,6 +1402,8 @@ static void mmci_dt_populate_generic_pdata(struct device_node *np,
 		pdata->sigdir |= MCI_ST_DATA74DIREN;
 	if (of_get_property(np, "st,sig-dir-cmd", NULL))
 		pdata->sigdir |= MCI_ST_CMDDIREN;
+	if (of_get_property(np, "st,sig-pin-fbclk", NULL))
+		pdata->sigdir |= MCI_ST_FBCLKEN;
 
 	pdata->gpio_wp = of_get_named_gpio(np, "wp-gpios", 0);
 	pdata->gpio_cd = of_get_named_gpio(np, "cd-gpios", 0);