cpufreq: mediatek-hw: Add support for MT8196

cpufreq: mediatek-hw: Add support for MT8196

The MT8196 SoC uses DVFS to set a desired target frequency for each CPU
core. It also uses slightly different register offsets.

Add support for it, which necessitates reworking how the mmio regs are
acquired, as mt8196 has the fdvfs register before the performance domain
registers.

I've verified with both `sysbench cpu run` and `head -c 10G \
/dev/urandom | pigz -p 8 -c - | pv -ba > /dev/null` that we don't just
get a higher reported clock frequency, but that the observed performance
also increases, by a factor of 2.64 in an 8 thread sysbench test.

Signed-off-by: Nicolas Frattaroli <nicolas.frattaroli@collabora.com>
Reviewed-by: AngeloGioacchino Del Regno <angelogiaocchino.delregno@collabora.com>
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>