drm/i915/pmu: Turn off the timer to sample frequencies when GT is parked

pmu_needs_timer() keeps the timer running even when GT is parked,
ostensibly to sample requested/actual frequencies. However
frequency_sample() has the following:

	/* Report 0/0 (actual/requested) frequency while parked. */
	if (!intel_gt_pm_get_if_awake(gt))
		return;

The above code prevents frequencies to be sampled while the GT is
parked. So we might as well turn off the sampling timer itself in this
case and save CPU cycles/power.

v2: Instead of turning freq bits off, return false, since no counters will
    run after this change when GT is parked (Tvrtko)
v3: Remove gpu_active argument of pmu_needs_timer (Andrzej)

Signed-off-by: Ashutosh Dixit <ashutosh.dixit@intel.com>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Reviewed-by: Andrzej Hajda <andrzej.hajda@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230524215629.97920-2-ashutosh.dixit@intel.com