cpufreq: intel_pstate: Drop ->update_util from pstate_funcs

All systems use the same P-state selection "powersave" algorithm
in the active mode if HWP is not used, so there's no need to provide
a pointer for it in struct pstate_funcs any more.

Drop ->update_util from struct pstate_funcs and make
intel_pstate_set_update_util_hook() use intel_pstate_update_util()
directly.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>