drm/xe/xe_pmu: Add PMU support for engine activity

drm/xe/xe_pmu: Add PMU support for engine activity

PMU provides two counters (engine-active-ticks, engine-total-ticks)
to calculate engine activity. When querying engine activity,
user must group these 2 counters using the perf_event
group mechanism to ensure both counters are sampled together.

To list the events

	./perf list
	  xe_0000_03_00.0/engine-active-ticks/	[Kernel PMU event]
	  xe_0000_03_00.0/engine-total-ticks/	[Kernel PMU event]

The formats to be used with the above are

	engine_instance	- config:12-19
	engine_class	- config:20-27
	gt		- config:60-63

The events can then be read using perf tool

./perf stat -e xe_0000_03_00.0/engine-active-ticks,gt=0,
			       engine_class=0,engine_instance=0/,
	       xe_0000_03_00.0/engine-total-ticks,gt=0,
			       engine_class=0,engine_instance=0/ -I 1000

Engine activity can then be calculated as below
engine activity % = (engine active ticks/engine total ticks) * 100

v2: validate gt
    rename total-ticks to engine-total-ticks
    add helper to get hwe (Umesh)

v3: fix checkpatch warning
    add details to documentation (Umesh)
    remove ascii formats from documentation (Lucas)

v4: remove unnecessary warn within raw_spinlock (Lucas)

Signed-off-by: Riana Tauro <riana.tauro@intel.com>
Reviewed-by: Umesh Nerlige Ramappa <umesh.nerlige.ramappa@intel.com>
Reviewed-by: Lucas De Marchi <lucas.demarchi@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20250224053903.2253539-5-riana.tauro@intel.com
Signed-off-by: Lucas De Marchi <lucas.demarchi@intel.com>