drm/i915: Wait longer for threads in migrate selftest on CHV/BXT+VTD

drm/i915: Wait longer for threads in migrate selftest on CHV/BXT+VTD

When running on a Cherryview, or on a Broxton with VTD enabled, pinning of
a VMA to GGTT is now committed asynchronously to avoid lock inversion
among reservation_ww and cpu_hotplug locks, the latter acquired from
stop_machine().  That may defer further processing of resources that
depend on that VMA.  As a consequence, a 10ms delay in a multithreaded
migrate test case may occur too short and still incomplete threads may be
interrupted, and the test case may fail with -ERESTARTSYS or -EINTR error
code returned by any of those threads.

Extend the delay to empirically determined 100ms on affected platforms.

v3: Add an in-line comment that explains why 100ms (Andi).
v2: Fix spelling (Sebastian, Krzysztof),
  - explain why VMA pinning is commited asynchronously on CHV/BXT+VTD
    (Krzysztof).

Cc: Andi Shyti <andi.shyti@kernel.org>
Signed-off-by: Janusz Krzysztofik <janusz.krzysztofik@linux.intel.com>
Reviewed-by: Sebastian Brzezinka <sebastian.brzezinka@intel.com>
Reviewed-by: Krzysztof Karas <krzysztof.karas@intel.com>
Acked-by: Andi Shyti <andi.shyti@linux.intel.com>
Signed-off-by: Andi Shyti <andi.shyti@linux.intel.com>
Link: https://lore.kernel.org/r/20251023082925.351307-7-janusz.krzysztofik@linux.intel.com