ipq806x: support independent core clocks in cpufreq with kernel 4.9+

Add back support for the independent_clocks definition that has been
removed between kernel 4.4 and 4.9 by upstream commits
eb96924acddc709db58221c210ca05cd9effb1df and
e86eee6bc2aaa6b3637f6497b26beee09a91bde9

* extend the new cpufreq_dt_platform_data definition in cpufreq-dt.h
* revert the removal of its usage in cpufreq-dt.c
* use new cpufreq-dt.h in qcom-cpufreq.c

Signed-off-by: Hannu Nyman <hannu.nyman@iki.fi>