ARM: shmobile: Add DT bindings for Renesas memory controllers

DT bindings for Renesas R-Mobile and SH-Mobile memory controllers

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Renesas R-Mobile and SH-Mobile SoCs contain one or more memory controllers.

These memory controllers differ from one SoC variant to another, and are called

by different names ("DDR Bus Controller (DBSC)", "DDR3 Bus State Controller

(DBSC3)", "SDRAM Bus State Controller (SBSC)").

Currently memory controller device nodes are used only to reference PM

domains, and prevent these PM domains from being powered down, which would

crash the system.

As there exist no actual drivers for these controllers yet, these bindings

should be considered EXPERIMENTAL for now.

Required properties:

  - compatible: Must be one of the following SoC-specific values:

		  - "renesas,dbsc-r8a73a4" (R-Mobile APE6)

		  - "renesas,dbsc3-r8a7740" (R-Mobile A1)

		  - "renesas,sbsc-sh73a0" (SH-Mobile AG5)

  - reg: Must contain the base address and length of the memory controller's

	 registers.

Optional properties:

  - interrupts: Must contain a list of interrupt specifiers for memory

		controller interrupts, if available.

  - interrupts-names: Must contain a list of interrupt names corresponding to

		      the interrupts in the interrupts property, if available.

		      Valid interrupt names are:

			- "sec" (secure interrupt)

			- "temp" (normal (temperature) interrupt)

  - power-domains: Must contain a reference to the PM domain that the memory

		   controller belongs to, if available.

Example:

	sbsc1: memory-controller@fe400000 {

		compatible = "renesas,sbsc-sh73a0";

		reg = <0xfe400000 0x400>;

		interrupts = <0 35 IRQ_TYPE_LEVEL_HIGH>,

			     <0 36 IRQ_TYPE_LEVEL_HIGH>;

		interrupt-names = "sec", "temp";

		power-domains = <&pd_a4bc0>;

	};