ARM: sun6i: a31: Add support for the High Speed Timers

The Allwinner A31 has support for four high speed timers. Apart for the
number of timers (4 vs 2), it's basically the same logic than the high
speed timers found in the sun5i chips.

Now that we have a driver to support it, we can enable them in the
device tree.

Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>