clocksource: Provide timekeeping for efm32 SoCs

An efm32 features 4 16-bit timers with a 10-bit prescaler. This driver
provides clocksource and clock event device using one timer instance
each.

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>

Documentation/devicetree/bindings/timer/efm32,timer.txt

@@ -0,0 +1,23 @@
+* EFM32 timer hardware
+
+The efm32 Giant Gecko SoCs come with four 16 bit timers. Two counters can be
+connected to form a 32 bit counter. Each timer has three Compare/Capture
+channels and can be used as PWM or Quadrature Decoder. Available clock sources
+are the cpu's HFPERCLK (with a 10-bit prescaler) or an external pin.
+
+Required properties:
+- compatible : Should be efm32,timer
+- reg : Address and length of the register set
+- clocks : Should contain a reference to the HFPERCLK
+
+Optional properties:
+- interrupts : Reference to the timer interrupt
+
+Example:
+
+timer@40010c00 {
+	compatible = "efm32,timer";
+	reg = <0x40010c00 0x400>;
+	interrupts = <14>;
+	clocks = <&cmu clk_HFPERCLKTIMER3>;
+};