clk: new driver for efm32 SoC

This patch adds support for the clocks provided by the Clock Management
Unit of Energy Micro's efm32 Giant Gecko SoCs including device tree
bindings.

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Mike Turquette <mturquette@linaro.org>

diff --cc Documentation/devicetree/bindings/clock/efm32-clock.txt
Simple merge

diff --cc drivers/clk/Makefile
Simple merge

diff --cc drivers/clk/clk-efm32gg.c
Simple merge

diff --cc include/dt-bindings/clock/efm32-cmu.h
Simple merge