ARM: tegra: nexus7: Improve CPU passive-cooling threshold

The current CPU thermal limit is a bit inappropriate for Nexus 7 once
device is getting used on a daily bases. For example, currently it's may
be impossible to watch a hardware accelerated 720p video without hitting
a severe CPU throttling, which ruins user experience. This patch improves
the thermal throttling thresholds.

In my experience setting CPU thermal threshold to 57C provides the most
reasonable result, where device is a bit warm under constant load and
not getting overly hot, in the same time performance is okay. Let's bump
the passive-cooling threshold from 50C to 57C and also lower the thermal
hysteresis to 0.2C in order to make throttling more reactive.

Signed-off-by: Dmitry Osipenko <digetx@gmail.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>