The time-efm32 driver uses the clocksource MMIO functions.
Thus it needs to select CLKSRC_MMIO in Kconfig.
Signed-off-by: Axel Lin <axel.lin@ingics.com> Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org> Acked-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>