clocksource/drivers/tegra: Lower clocksource rating for some Tegra's

Arch-timer is more preferable for a range of Tegra SoC generations as
it has higher precision and is not affect by any kind of problems.

Pointed-out-by: Peter De Schrijver <pdeschrijver@nvidia.com>
Signed-off-by: Dmitry Osipenko <digetx@gmail.com>
Acked-By: Peter De Schrijver <pdeschrijver@nvidia.com>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>