dt-bindings: ata: add DT bindings for ahci-dm816 SATA controller

Device tree binding for the TI DM816 AHCI SATA Controller

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Required properties:

  - compatible: must be "ti,dm816-ahci"

  - reg: physical base address and size of the register region used by

         the controller (as defined by the AHCI 1.1 standard)

  - interrupts: interrupt specifier (refer to the interrupt binding)

  - clocks: list of phandle and clock specifier pairs (or only

            phandles for clock providers with '0' defined for

            #clock-cells); two clocks must be specified: the functional

            clock and an external reference clock

Example:

	sata: sata@4a140000 {

		compatible = "ti,dm816-ahci";

		reg = <0x4a140000 0x10000>;

		interrupts = <16>;

		clocks = <&sysclk5_ck>, <&sata_refclk>;

	};