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>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Giovanni Gherdovich <ggherdovich@suse.cz>
Cc: "Rafael J. Wysocki" <rjw@rjwysocki.net>