clocksource/drivers/sun5i: Refactor the current code

Refactor the code in order to remove the global variables and
split the clock source and clock events registration in order to
ease the addition of the clock notifiers needed to handle the
parent clock rate changes.

Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Cc: linux-arm-kernel@lists.infradead.org
Link: http://lkml.kernel.org/r/1427796746-373-4-git-send-email-daniel.lezcano@linaro.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>