drm/i915: Allocate intel_engine_coredump_alloc with ALLOW_FAIL

Allocate intel_engine_coredump_alloc with ALLOW_FAIL rather than
GFP_KERNEL to fully decouple the error capture from fence signalling.

v2:
 (John Harrison)
  - Fix typo in commit message (s/do/to)

Fixes: 8b91cdd4 ("drm/i915: Use __GFP_KSWAPD_RECLAIM in the capture code")

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/20220121043118.24886-2-matthew.brost@intel.com