ARM Versatile Express system registers
--------------------------------------

This is a system control registers block, providing multiple low level
platform functions like board detection and identification, software
interrupt generation, MMC and NOR Flash control etc.

Required node properties:
- compatible value : = "arm,vexpress,sysreg";
- reg : physical base address and the size of the registers window
- gpio-controller : specifies that the node is a GPIO controller
- #gpio-cells : size of the GPIO specifier, should be 2:
  - first cell is the pseudo-GPIO line number:
    0 - MMC CARDIN
    1 - MMC WPROT
    2 - NOR FLASH WPn
  - second cell can take standard GPIO flags (currently ignored).

Example:
	v2m_sysreg: sysreg@10000000 {
 		compatible = "arm,vexpress-sysreg";
 		reg = <0x10000000 0x1000>;
		gpio-controller;
		#gpio-cells = <2>;
 	};

This block also can also act a bridge to the platform's configuration
bus via "system control" interface, addressing devices with site number,
position in the board stack, config controller, function and device
numbers - see motherboard's TRM for more details.

The node describing a config device must refer to the sysreg node via
"arm,vexpress,config-bridge" phandle (can be also defined in the node's
parent) and relies on the board topology properties - see main vexpress
node documentation for more details. It must must also define the
following property:
- arm,vexpress-sysreg,func : must contain two cells:
  - first cell defines function number (eg. 1 for clock generator,
    2 for voltage regulators etc.)
  - device number (eg. osc 0, osc 1 etc.)

Example:
	mcc {
		arm,vexpress,config-bridge = <&v2m_sysreg>;

		osc@0 {
			compatible = "arm,vexpress-osc";
			arm,vexpress-sysreg,func = <1 0>;
		};
	};