cpufreq: dt-platdev: block SDM670 in cpufreq-dt-platdev

The Snapdragon 670 uses the Qualcomm driver for CPU frequency scaling.
Block this driver from loading on it so the driver does not pollute
dmesg with an error.

Signed-off-by: Richard Acayan <mailingradian@gmail.com>
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>