drm/i915: Add logical engine mapping

Add logical engine mapping. This is required for split-frame, as
workloads need to be placed on engines in a logically contiguous manner.

v2:
 (Daniel Vetter)
  - Add kernel doc for new fields
v3:
 (Tvrtko)
  - Update comment for new logical_mask field
v4:
 (John Harrison)
  - Update comment for new logical_mask field

Signed-off-by: Matthew Brost <matthew.brost@intel.com>
Reviewed-by: John Harrison <John.C.Harrison@Intel.com>
Signed-off-by: John Harrison <John.C.Harrison@Intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20211014172005.27155-6-matthew.brost@intel.com