drm/i915/guc: GuC virtual engines

Implement GuC virtual engines. Rather simple implementation, basically
just allocate an engine, setup context enter / exit function to virtual
engine specific functions, set all other variables / functions to guc
versions, and set the engine mask to that of all the siblings.

v2: Update to work with proto-ctx
v3:
 (Daniele)
  - Drop include, add comment to intel_virtual_engine_has_heartbeat

Cc: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Signed-off-by: Matthew Brost <matthew.brost@intel.com>
Reviewed-by: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Signed-off-by: John Harrison <John.C.Harrison@Intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210727002348.97202-2-matthew.brost@intel.com