Documentation: samsung-phy: Add exynos-pcie-phy binding

Add the exynos-pcie-phy binding for Exynos PCIe PHY.  This is for using
generic PHY framework.
Signed-off-by: NJaehoon Chung <jh80.chung@samsung.com>
Signed-off-by: NBjorn Helgaas <bhelgaas@google.com>
Acked-by: NRob Herring <robh@kernel.org>

Documentation/devicetree/bindings/phy/samsung-phy.txt

@@ -191,3 +191,20 @@ Example:
 		usbdrdphy0 = &usb3_phy0;
 		usbdrdphy1 = &usb3_phy1;
 	};
+
+Samsung Exynos SoC series PCIe PHY controller
+--------------------------------------------------
+Required properties:
+- compatible : Should be set to "samsung,exynos5440-pcie-phy"
+- #phy-cells : Must be zero
+- reg : a register used by phy driver.
+	- First is for phy register, second is for block register.
+- reg-names : Must be set to "phy" and "block".
+
+Example:
+	pcie_phy0: pcie-phy@270000 {
+		#phy-cells = <0>;
+		compatible = "samsung,exynos5440-pcie-phy";
+		reg = <0x270000 0x1000>, <0x271000 0x40>;
+		reg-names = "phy", "block";
+	};