devicetree:bindings: add devicetree bindings for ceva ahci

adds bindings for CEVA AHCI SATA controller. optional property
broken-gen2 is useful incase of hardware speed limitation.
Signed-off-by: Suneel Garapati <suneel.garapati@xilinx.com>
Signed-off-by: Tejun Heo <tj@kernel.org>

Documentation/devicetree/bindings/ata/ahci-ceva.txt

+Binding for CEVA AHCI SATA Controller
+
+Required properties:
+  - reg: Physical base address and size of the controller's register area.
+  - compatible: Compatibility string. Must be 'ceva,ahci-1v84'.
+  - clocks: Input clock specifier. Refer to common clock bindings.
+  - interrupts: Interrupt specifier. Refer to interrupt binding.
+
+Optional properties:
+  - ceva,broken-gen2: limit to gen1 speed instead of gen2.
+
+Examples:
+	ahci@fd0c0000 {
+		compatible = "ceva,ahci-1v84";
+		reg = <0xfd0c0000 0x200>;
+		interrupt-parent = <&gic>;
+		interrupts = <0 133 4>;
+		clocks = <&clkc SATA_CLK_ID>;
+		ceva,broken-gen2;
+	};