ARM: socfpga: add bindings document for fpga bridge drivers

Altera FPGA To SDRAM Bridge Driver

Required properties:

- compatible		: Should contain "altr,socfpga-fpga2sdram-bridge"

Optional properties:

- bridge-enable		: 0 if driver should disable bridge at startup

			  1 if driver should enable bridge at startup

			  Default is to leave bridge in current state.

Example:

	fpga_bridge3: fpga-bridge@ffc25080 {

		compatible = "altr,socfpga-fpga2sdram-bridge";

		reg = <0xffc25080 0x4>;

		bridge-enable = <0>;

	};

Altera FPGA/HPS Bridge Driver

Required properties:

- regs		: base address and size for AXI bridge module

- compatible	: Should contain one of:

		  "altr,socfpga-lwhps2fpga-bridge",

		  "altr,socfpga-hps2fpga-bridge", or

		  "altr,socfpga-fpga2hps-bridge"

- resets	: Phandle and reset specifier for this bridge's reset

- clocks	: Clocks used by this module.

Optional properties:

- bridge-enable	: 0 if driver should disable bridge at startup.

		  1 if driver should enable bridge at startup.

		  Default is to leave bridge in its current state.

Example:

	fpga_bridge0: fpga-bridge@ff400000 {

		compatible = "altr,socfpga-lwhps2fpga-bridge";

		reg = <0xff400000 0x100000>;

		resets = <&rst LWHPS2FPGA_RESET>;

		clocks = <&l4_main_clk>;

		bridge-enable = <0>;

	};

	fpga_bridge1: fpga-bridge@ff500000 {

		compatible = "altr,socfpga-hps2fpga-bridge";

		reg = <0xff500000 0x10000>;

		resets = <&rst HPS2FPGA_RESET>;

		clocks = <&l4_main_clk>;

		bridge-enable = <1>;

	};

	fpga_bridge2: fpga-bridge@ff600000 {

		compatible = "altr,socfpga-fpga2hps-bridge";

		reg = <0xff600000 0x100000>;

		resets = <&rst FPGA2HPS_RESET>;

		clocks = <&l4_main_clk>;

	};