clocksource/drivers/sun4i: Switch to the timer-of common init

Previously a framework to factor out the drivers init function has been
merged.

Use this common framework in this driver, we get:

Before:

text    data     bss     dec   hex filename
1787     384      12    2183   887 drivers/clocksource/sun4i_timer.o

After:

text    data     bss     dec   hex filename
1407     512       0    1919   77f drivers/clocksource/sun4i_timer.o

Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Tested-by: Chen-Yu Tsai <wens@csie.org>
diff --git a/drivers/clocksource/Kconfig b/drivers/clocksource/Kconfig
index 4be163b..88818a4 100644
--- a/drivers/clocksource/Kconfig
+++ b/drivers/clocksource/Kconfig
@@ -108,6 +108,7 @@
 	depends on GENERIC_CLOCKEVENTS
 	depends on HAS_IOMEM
 	select CLKSRC_MMIO
+	select TIMER_OF
 	help
 	  Enables support for the Sun4i timer.