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>