cpufreq: Add SM6115 to cpufreq-dt-platdev blocklist

The Qualcomm SM6115 platform uses the
qcom-cpufreq-hw driver, so add it to the cpufreq-dt-platdev driver's
blocklist.

Signed-off-by: Adam Skladowski <a39.skl@gmail.com>
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>