cpufreq: exynos: Broadcast frequency change notifications for all cores

On Exynos SoCs all cores share the same frequency setting, so changing
frequency of one core will affect rest of cores.

This patch modifies the exynos-cpufreq driver to inform cpufreq core
about this behavior and broadcast frequency change notifications for all
cores.

Signed-off-by: Tomasz Figa <t.figa@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>