intel_idle: refactor state->enter manipulation into its own function

JIRA: https://issues.redhat.com/browse/RHEL-11351



commit 4622ba92
Author: Arjan van de Ven <arjan@linux.intel.com>
Date:   Mon Jun 5 15:47:13 2023 +0000

    intel_idle: refactor state->enter manipulation into its own function

    Since the 6.4 kernel, the logic for updating a state's enter method
    based on "environmental conditions" (command line options, cpu sidechannel
    workarounds etc etc) has gotten pretty complex.
    This patch refactors this into a seperate small, self contained function
    (no behavior changes) for improved readability and to make future
    changes to this logic easier to do and understand.

Signed-off-by: Arjan van de Ven <arjan@linux.intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

Signed-off-by: David Arcari <darcari@redhat.com>