cpufreq: sti-cpufreq: add stih418 support

[ Upstream commit 01a163c52039e9426c7d3d3ab16ca261ad622597 ]

The STiH418 can be controlled the same way as STiH407 &
STiH410 regarding cpufreq.

Signed-off-by: Alain Volmat <avolmat@me.com>
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>