clk: samsung: Make exynos850_register_cmu shared

Rename exynos850_register_cmu to exynos_arm64_register_cmu and move it
to a new file called "clk-exynos-arm64.c".

This should have no functional changes, but it will allow this code to
be shared between other arm64 Exynos SoCs, like the Exynos7885 and
possibly ExynosAuto V9.

Signed-off-by: David Virag <virag.david003@gmail.com>
Signed-off-by: Sylwester Nawrocki <s.nawrocki@samsung.com>
Reviewed-by: Sam Protsenko <semen.protsenko@linaro.org>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
Link: https://lore.kernel.org/r/20211206153124.427102-5-virag.david003@gmail.com