cpufreq: s3c24xx: move low-level clk reg access into platform code

Rather than have the cpufreq drivers touch include the
common headers to get the constants, add a small indirection.
This is still not the proper way that would do this through
the common clk API, but it lets us kill off the header file
usage.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
Link: https://lore.kernel.org/r/20200806182059.2431-37-krzk@kernel.org


[krzk: Rebase and fix -Wold-style-definition]
Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>