drm/i915/guc: Implement multi-lrc submission

Implement multi-lrc submission via a single workqueue entry and single
H2G. The workqueue entry contains an updated tail value for each
request, of all the contexts in the multi-lrc submission, and updates
these values simultaneously. As such, the tasklet and bypass path have
been updated to coalesce requests into a single submission.

v2:
 (John Harrison)
  - s/wqe/wqi
  - Use FIELD_PREP macros
  - Add GEM_BUG_ONs ensures length fits within field
  - Add comment / white space to intel_guc_write_barrier
 (Kernel test robot)
  - Make need_tasklet a static function
v3:
 (Docs)
  - A comment for submission_stall_reason
v4:
 (Kernel test robot)
  - Initialize return value in bypass tasklt submit function
 (John Harrison)
  - Add comment near work queue defs
  - Add BUILD_BUG_ON to ensure WQ_SIZE is a power of 2
  - Update write_barrier comment to talk about work queue
v5:
 (John Harrison)
  - Fix typo in work queue comment

Reviewed-by: John Harrison <John.C.Harrison@Intel.com>
Signed-off-by: Matthew Brost <matthew.brost@intel.com>
Signed-off-by: John Harrison <John.C.Harrison@Intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20211014172005.27155-13-matthew.brost@intel.com