mmc: sdhci-cadence: add Socionext UniPhier specific compatible string

Add a Socionext SoC specific compatible (suggested by Rob Herring).

No SoC specific data are associated with the compatible strings for
now, but other SoC vendors may use this IP and want to differentiate
IP variants in the future.
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>

Documentation/devicetree/bindings/mmc/sdhci-cadence.txt

 * Cadence SD/SDIO/eMMC Host Controller
 
 Required properties:
-- compatible: should be "cdns,sd4hc".
+- compatible: should be one of the following:
+    "cdns,sd4hc"               - default of the IP
+    "socionext,uniphier-sd4hc" - for Socionext UniPhier SoCs
 - reg: offset and length of the register set for the device.
 - interrupts: a single interrupt specifier.
 - clocks: phandle to the input clock.
@@ -19,7 +21,7 @@ if supported.  See mmc.txt for details.
 
 Example:
 	emmc: sdhci@5a000000 {
-		compatible = "cdns,sd4hc";
+		compatible = "socionext,uniphier-sd4hc", "cdns,sd4hc";
 		reg = <0x5a000000 0x400>;
 		interrupts = <0 78 4>;
 		clocks = <&clk 4>;

drivers/mmc/host/sdhci-cadence.c

@@ -262,6 +262,7 @@ static int sdhci_cdns_probe(struct platform_device *pdev)
 }
 
 static const struct of_device_id sdhci_cdns_match[] = {
+	{ .compatible = "socionext,uniphier-sd4hc" },
 	{ .compatible = "cdns,sd4hc" },
 	{ /* sentinel */ }
 };