cpufreq: Add sun50i nvmem based CPU scaling driver

For some SoCs, the CPU frequency subset and voltage value of each OPP
varies based on the silicon variant in use. The sun50i-cpufreq-nvmem
driver reads the efuse value from the SoC to provide the OPP framework
with required information.

Signed-off-by: Yangtao Li <tiny.windzz@gmail.com>
Acked-by: Maxime Ripard <maxime.ripard@bootlin.com>
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>