cpufreq: dt-platdev: Blacklist ti,am625 SoC

Add ti,am625 SoC to the blacklist as the ti-cpufreq driver will handle
creating the cpufreq-dt platform device after it completes so it is not
created twice.

Signed-off-by: Dave Gerlach <d-gerlach@ti.com>
Signed-off-by: Vibhore Vardhan <vibhore@ti.com>
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>