drm/i915: Expose client engine utilisation 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 i915.

Example of the output:

  pos:    0
  flags:  0100002
  mnt_id: 21
  drm-driver: i915
  drm-pdev:   0000:00:02.0
  drm-client-id:      7
  drm-engine-render:  9288864723 ns
  drm-engine-copy:    2035071108 ns
  drm-engine-video:   0 ns
  drm-engine-video-enhance:   0 ns

v2:
 * Update for removal of name and pid.

v3:
 * Use drm_driver.name.

v4:
 * Added drm-engine-capacity- tag.
 * Fix typo. (Umesh)

v5:
 * Don't output engine data before Gen8.

Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Cc: David M Nieto <David.Nieto@amd.com>
Cc: Christian König <christian.koenig@amd.com>
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: Chris Healy <cphealy@gmail.com>
Acked-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Umesh Nerlige Ramappa <umesh.nerlige.ramappa@intel.com>
Acked-by: Rob Clark <robdclark@gmail.com>
Acked-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20220401142205.3123159-9-tvrtko.ursulin@linux.intel.com