clk: samsung: Pull struct exynos_cpuclk into clk-cpu.c

clk: samsung: Pull struct exynos_cpuclk into clk-cpu.c

Reduce the scope of struct exynos_cpuclk, as it's only used in clk-cpu.c
internally. All drivers using clk-pll.h already include clk.h as well,
so this change doesn't break anything.

No functional change.

Signed-off-by: Sam Protsenko <semen.protsenko@linaro.org>
Link: https://lore.kernel.org/r/20240224202053.25313-4-semen.protsenko@linaro.org
Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>