media: dt-bindings: imx7-csi: Document a single CSI clock

- interrupts    : should contain CSI interrupt;

- clocks        : list of clock specifiers, see

        Documentation/devicetree/bindings/clock/clock-bindings.txt for details;

- clock-names   : must contain "axi", "mclk" and "dcic" entries, matching

                 entries in the clock property;

- clock-names   : must contain "mclk";

The device node shall contain one 'port' child node with one child 'endpoint'

node, according to the bindings defined in:

                        compatible = "fsl,imx7-csi";

                        reg = <0x30710000 0x10000>;

                        interrupts = <GIC_SPI 7 IRQ_TYPE_LEVEL_HIGH>;

                        clocks = <&clks IMX7D_CLK_DUMMY>,

                                        <&clks IMX7D_CSI_MCLK_ROOT_CLK>,

                                        <&clks IMX7D_CLK_DUMMY>;

                        clock-names = "axi", "mclk", "dcic";

                        clocks = <&clks IMX7D_CSI_MCLK_ROOT_CLK>;

                        clock-names = "mclk";

                        port {

                                csi_from_csi_mux: endpoint {