drm/msm: Expose client engine utilization via fdinfo

Similar to AMD commit
87444254

 ("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>