drm/msm: Expose client engine utilization via fdinfo

Similar to AMD commit
8744425411 ("drm/amdgpu: Add show_fdinfo() interface"), using the
infrastructure added in previous patches, we add basic client info
and GPU engine utilisation for msm.

Example output:

	# cat /proc/`pgrep glmark2`/fdinfo/6
	pos:	0
	flags:	02400002
	mnt_id:	21
	ino:	162
	drm-driver:	msm
	drm-client-id:	7
	drm-engine-gpu:	1734371319 ns
	drm-cycles-gpu:	1153645024
	drm-maxfreq-gpu:	800000000 Hz

See also: https://patchwork.freedesktop.org/patch/468505/

v2: Add dev-maxfreq-$engine and update drm-usage-stats.rst
v3: spelling and compiler warning

Signed-off-by: Rob Clark <robdclark@chromium.org>
Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Acked-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Patchwork: https://patchwork.freedesktop.org/patch/488906/
Link: https://lore.kernel.org/r/20220609174213.2265938-2-robdclark@gmail.com
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>

Documentation/gpu/drm-usage-stats.rst

@@ -105,6 +105,27 @@ object belong to this client, in the respective memory region.
 Default unit shall be bytes with optional unit specifiers of 'KiB' or 'MiB'
 indicating kibi- or mebi-bytes.
 
+- drm-cycles-<str> <uint>
+
+Engine identifier string must be the same as the one specified in the
+drm-engine-<str> tag and shall contain the number of busy cycles for the given
+engine.
+
+Values are not required to be constantly monotonic if it makes the driver
+implementation easier, but are required to catch up with the previously reported
+larger value within a reasonable period. Upon observing a value lower than what
+was previously read, userspace is expected to stay with that larger previous
+value until a monotonic update is seen.
+
+- drm-maxfreq-<str> <uint> [Hz|MHz|KHz]
+
+Engine identifier string must be the same as the one specified in the
+drm-engine-<str> tag and shall contain the maximum frequency for the given
+engine.  Taken together with drm-cycles-<str>, this can be used to calculate
+percentage utilization of the engine, whereas drm-engine-<str> only reflects
+time active without considering what frequency the engine is operating as a
+percentage of it's maximum frequency.
+
 ===============================
 Driver specific implementations
 ===============================