Introduce 'set parallel submit' extension to connect UAPI to GuC
multi-lrc interface. Kernel doc in new uAPI should explain it all.

IGT: https://patchwork.freedesktop.org/patch/447008/?series=93071&rev=1
media UMD: https://github.com/intel/media-driver/pull/1252

v2:
 (Daniel Vetter)
  - Add IGT link and placeholder for media UMD link
v3:
 (Kernel test robot)
  - Fix warning in unpin engines call
 (John Harrison)
  - Reword a bunch of the kernel doc
v4:
 (John Harrison)
  - Add comment why perma-pin is done after setting gem context
  - Update some comments / docs for proto contexts
v5:
 (John Harrison)
  - Rework perma-pin comment
  - Add BUG_IN if context is pinned when setting gem context

Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
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/20211014172005.27155-17-matthew.brost@intel.com