x86, ACPI: rename init_freq_invariance_cppc() to arch_init_invariance_cppc()

init_freq_invariance_cppc() was called in acpi_cppc_processor_probe(),
after CPU performance information and controls were populated from the
per-cpu _CPC objects.

But these _CPC objects provide information that helps with both CPU
(u-arch) and frequency invariance. Therefore, change the function name
to a more generic one, while adding the arch_ prefix, as this function
is expected to be defined differently by different architectures.

Signed-off-by: Ionela Voinescu <ionela.voinescu@arm.com>
Acked-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Tested-by: Valentin Schneider <valentin.schneider@arm.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>