cpufreq: qcom-nvmem: add support for IPQ6018

IPQ6018 SoC series comes in multiple SKU-s, and not all of them support
high frequency OPP points.

SoC itself does however have a single bit in QFPROM to indicate the CPU
speed-bin.
That bit is used to indicate frequency limit of 1.5GHz, but that alone is
not enough as IPQ6000 only goes up to 1.2GHz, but SMEM ID can be used to
limit it further.

IPQ6018 compatible is blacklisted from DT platdev as the cpufreq device
will get created by NVMEM CPUFreq driver.

Signed-off-by: Robert Marko <robimarko@gmail.com>
[ Viresh: Fixed rebase conflict. ]
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>