Required properties:
-- compatible : should be "brcm,bcm2835-system-timer.txt"
+- compatible : should be "brcm,bcm2835-system-timer"
- reg : Specifies base physical address and size of the registers.
- interrupts : A list of 4 interrupt sinks; one per timer channel.
- clock-frequency : The frequency of the clock that drives the counter, in Hz.