clocksource: time-efm32: Select CLKSRC_MMIO
clocksource: time-efm32: Select CLKSRC_MMIO

The time-efm32 driver uses the clocksource MMIO functions.
Thus it needs to select CLKSRC_MMIO in Kconfig.

Signed-off-by: Axel Lin <b6ffd6973e972cb999e8e535ab74da7fee0c035f@ingics.com>
Signed-off-by: Daniel Lezcano <e9fa45941f2ebe89c1b9d6c5f339ab42eadb8567@linaro.org>
Acked-by: Uwe Kleine-König <181323dd666a182bc2d953e52d0ac3ab54cd8391@pengutronix.de>

KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs