dt-bindings: mmc: add DT binding for UniPhier SD/eMMC controller

UniPhier SD/eMMC controller

Required properties:

- compatible: should be one of the following:

    "socionext,uniphier-sd-v2.91"  - IP version 2.91

    "socionext,uniphier-sd-v3.1"   - IP version 3.1

    "socionext,uniphier-sd-v3.1.1" - IP version 3.1.1

- reg: offset and length of the register set for the device.

- interrupts: a single interrupt specifier.

- clocks: a single clock specifier of the controller clock.

- reset-names: should contain the following:

    "host"   - mandatory for all versions

    "bridge" - should exist only for "socionext,uniphier-sd-v2.91"

    "hw"     - should exist if eMMC hw reset line is available

- resets: a list of reset specifiers, corresponding to the reset-names

Optional properties:

- pinctrl-names: if present, should contain the following:

    "default" - should exist for all instances

    "uhs"     - should exist for SD instance with UHS support

- pinctrl-0: pin control state for the default mode

- pinctrl-1: pin control state for the UHS mode

- dma-names: should be "rx-tx" if present.

  This property can exist only for "socionext,uniphier-sd-v2.91".

- dmas: a single DMA channel specifier

  This property can exist only for "socionext,uniphier-sd-v2.91".

- bus-width: see mmc.txt

- cap-sd-highspeed: see mmc.txt

- cap-mmc-highspeed: see mmc.txt

- sd-uhs-sdr12: see mmc.txt

- sd-uhs-sdr25: see mmc.txt

- sd-uhs-sdr50: see mmc.txt

- cap-mmc-hw-reset: should exist if reset-names contains "hw". see mmc.txt

- non-removable: see mmc.txt

Example:

	sd: sdhc@5a400000 {

		compatible = "socionext,uniphier-sd-v2.91";

		reg = <0x5a400000 0x200>;

		interrupts = <0 76 4>;

		pinctrl-names = "default", "uhs";

		pinctrl-0 = <&pinctrl_sd>;

		pinctrl-1 = <&pinctrl_sd_uhs>;

		clocks = <&mio_clk 0>;

		reset-names = "host", "bridge";

		resets = <&mio_rst 0>, <&mio_rst 3>;

		dma-names = "rx-tx";

		dmas = <&dmac 4>;

		bus-width = <4>;

		cap-sd-highspeed;

		sd-uhs-sdr12;

		sd-uhs-sdr25;

		sd-uhs-sdr50;

	};