ACPI: processor: Refine messages in acpi_early_processor_control_setup()

The source and meaning of the messages printed by
acpi_early_processor_control_setup() is unclear, so add a pr_fmt()
definition to acpi_processor.c and expand the messages to make it
clear that they are about CPUs.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Reviewed-by: Michal Wilczynski <michal.wilczynski@intel.com>