clocksource: sun4i: Select CLKSRC_MMIO

The Allwinner SoCs timer use the clocksource MMIO functions. We thus
need to select them in Kconfig.

Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
diff --git a/drivers/clocksource/Kconfig b/drivers/clocksource/Kconfig
index 915a388..bdb953e 100644
--- a/drivers/clocksource/Kconfig
+++ b/drivers/clocksource/Kconfig
@@ -34,6 +34,7 @@
 	bool
 
 config SUN4I_TIMER
+	select CLKSRC_MMIO
 	bool
 
 config VT8500_TIMER