UniPhier outer cache controller

UniPhier SoCs are integrated with a full-custom outer cache controller system.
All of them have a level 2 cache controller, and some have a level 3 cache
controller as well.

Required properties:
- compatible: should be "socionext,uniphier-system-cache"
- reg: offsets and lengths of the register sets for the device.  It should
  contain 3 regions: control register, revision register, operation register,
  in this order.
- cache-unified: specifies the cache is a unified cache.
- cache-size: specifies the size in bytes of the cache
- cache-sets: specifies the number of associativity sets of the cache
- cache-line-size: specifies the line size in bytes
- cache-level: specifies the level in the cache hierarchy.  The value should
  be 2 for L2 cache, 3 for L3 cache, etc.

Optional properties:
- next-level-cache: phandle to the next level cache if present.  The next level
  cache should be also compatible with "socionext,uniphier-system-cache".

The L2 cache must exist to use the L3 cache; the cache hierarchy must be
indicated correctly with "next-level-cache" properties.

Example 1 (system with L2):
	l2: l2-cache@500c0000 {
		compatible = "socionext,uniphier-system-cache";
		reg = <0x500c0000 0x2000>, <0x503c0100 0x4>,
		      <0x506c0000 0x400>;
		cache-unified;
		cache-size = <0x80000>;
		cache-sets = <256>;
		cache-line-size = <128>;
		cache-level = <2>;
	};

Example 2 (system with L2 and L3):
	l2: l2-cache@500c0000 {
		compatible = "socionext,uniphier-system-cache";
		reg = <0x500c0000 0x2000>, <0x503c0100 0x8>,
		      <0x506c0000 0x400>;
		cache-unified;
		cache-size = <0x200000>;
		cache-sets = <512>;
		cache-line-size = <128>;
		cache-level = <2>;
		next-level-cache = <&l3>;
	};

	l3: l3-cache@500c8000 {
		compatible = "socionext,uniphier-system-cache";
		reg = <0x500c8000 0x2000>, <0x503c8100 0x8>,
		      <0x506c8000 0x400>;
		cache-unified;
		cache-size = <0x400000>;
		cache-sets = <512>;
		cache-line-size = <256>;
		cache-level = <3>;
	};