cpufreq: Add Tegra234 to cpufreq-dt-platdev blocklist

Tegra234 platform uses the tegra194-cpufreq driver, so add it
to the blocklist in cpufreq-dt-platdev driver to avoid the cpufreq
driver registration from there.

Signed-off-by: Sumit Gupta <sumitg@nvidia.com>
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>