ARM: tegra: Enable CPUFREQ userspace governor

Enable the CPUFREQ userspace governor in the tegra_defconfig so that
we can test CPUFREQ with the userspace governor with this configuration
on 32-bit Tegra devices.

Signed-off-by: Jon Hunter <jonathanh@nvidia.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>