dt-bindings: Amlogic: Add Meson8 and Meson8b SMP related documentation

Amlogic Meson8 and Meson8b power-management-unit:

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The pmu is used to turn off and on different power domains of the SoCs

This includes the power to the CPU cores.

Required node properties:

- compatible value : depending on the SoC this should be one of:

			"amlogic,meson8-pmu"

			"amlogic,meson8b-pmu"

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

Example:

	pmu@c81000e4 {

		compatible = "amlogic,meson8b-pmu", "syscon";

		reg = <0xc81000e0 0x18>;

	};

Amlogic Meson8 and Meson8b SRAM for smp bringup:

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Amlogic's SMP-capable SoCs use part of the sram for the bringup of the cores.

Once the core gets powered up it executes the code that is residing at a

specific location.

Therefore a reserved section sub-node has to be added to the mmio-sram

declaration.

Required sub-node properties:

- compatible : depending on the SoC this should be one of:

		"amlogic,meson8-smp-sram"

		"amlogic,meson8b-smp-sram"

The rest of the properties should follow the generic mmio-sram discription

found in ../../misc/sram.txt

Example:

	sram: sram@d9000000 {

		compatible = "mmio-sram";

		reg = <0xd9000000 0x20000>;

		#address-cells = <1>;

		#size-cells = <1>;

		ranges = <0 0xd9000000 0x20000>;

		smp-sram@1ff80 {

			compatible = "amlogic,meson8b-smp-sram";

			reg = <0x1ff80 0x8>;

		};

	};

			    "actions,s500-smp"

			    "allwinner,sun6i-a31"

			    "allwinner,sun8i-a23"

			    "amlogic,meson8-smp"

			    "amlogic,meson8b-smp"

			    "arm,realview-smp"

			    "brcm,bcm11351-cpu-method"

			    "brcm,bcm23550"