OLPC AP-SP serio interface

Required properties:
- compatible : "olpc,ap-sp"
- reg : base address and length of SoC's WTM registers
- interrupts : SP-AP interrupt
- clocks : phandle + clock-specifier for the clock that drives the WTM
- clock-names:  should be "sp"

Example:
	ap-sp@d4290000 {
		compatible = "olpc,ap-sp";
		reg = <0xd4290000 0x1000>;
		interrupts = <40>;
		clocks = <&soc_clocks MMP2_CLK_SP>;
		clock-names = "sp";
	}