mmc: sdhci-pxav3: Document clocks and additional clock-names property

Now that sdhci-pxav3 driver allows to have more than one IP clock defined,
document both clocks and clock-names properties.

Signed-off-by: Sebastian Hesselbarth <[e-mail]>
Signed-off-by: Ulf Hansson <[e-mail]>

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

···
   * for "marvell,armada-380-sdhci", two register areas. The first one
     for the SDHCI registers themselves, and the second one for the
     AXI/Mbus bridge registers of the SDHCI unit.
+- clocks: Array of clocks required for SDHCI; requires at least one for
+    I/O clock.
+- clock-names: Array of names corresponding to clocks property; shall be
+    "io" for I/O clock and "core" for optional core clock.
 
 Optional properties:
 - mrvl,clk-delay-cycles: Specify a number of cycles to delay for tuning.
···
 	reg = <0xd4280800 0x800>;
 	bus-width = <8>;
 	interrupts = <27>;
+	clocks = <&chip CLKID_SDIO1XIN>, <&chip CLKID_SDIO1>;
+	clock-names = "io", "core";
 	non-removable;
 	mrvl,clk-delay-cycles = <31>;
 };
···
 	reg = <0xd8000 0x1000>, <0xdc000 0x100>;
 	interrupts = <0 25 0x4>;
 	clocks = <&gateclk 17>;
+	clock-names = "io";
 	mrvl,clk-delay-cycles = <0x1F>;
 };