dt-bindings: sram: convert rockchip-pmu-sram bindings to yaml

Rockchip SRAM for pmu:

------------------------------

The sram of pmu is used to store the function of resume from maskrom(the 1st

level loader). This is a common use of the "pmu-sram" because it keeps power

even in low power states in the system.

Required node properties:

- compatible : should be "rockchip,rk3288-pmu-sram"

- reg : physical base address and the size of the registers window

Example:

	sram@ff720000 {

		compatible = "rockchip,rk3288-pmu-sram", "mmio-sram";

		reg = <0xff720000 0x1000>;

	};

      enum:

        - mmio-sram

        - atmel,sama5d2-securam

        - rockchip,rk3288-pmu-sram

  reg:

    maxItems: 1

required:

  - compatible

  - reg

if:

  properties:

    compatible:

      contains:

        const: rockchip,rk3288-pmu-sram

else:

  required:

    - "#address-cells"

    - "#size-cells"

    - ranges

        };

    };

  - |

    // Rockchip's rk3288 SoC uses the sram of pmu to store the function of

    // resume from maskrom(the 1st level loader). This is a common use of

    // the "pmu-sram" because it keeps power even in low power states

    // in the system.

    sram@ff720000 {

      compatible = "rockchip,rk3288-pmu-sram", "mmio-sram";

      reg = <0xff720000 0x1000>;

    };

  - |

    // Allwinner's A80 SoC uses part of the secure sram for hotplugging of the

    // primary core (cpu0). Once the core gets powered up it checks if a magic