drm/i915/icl: Default to Thread Group preemption for compute workloads

We assumed that the default preemption granularity is fine for ICL.
Unfortunately, it turns out that some drivers don't support mid-thread
preemption for compute workloads.
If a workload that doesn't support mid-thread preemption gets mid-thread
preempted, we're going to observe a GPU hang.
While I'm here, let's also update the "workaround" naming.

Signed-off-by: Michał Winiarski <michal.winiarski@intel.com>
Cc: Anuj Phogat <anuj.phogat@intel.com>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Cc: Matt Roper <matthew.d.roper@intel.com>
Cc: Rafael Antognolli <rafael.antognolli@intel.com>
Tested-by: Anuj Phogat <anuj.phogat@intel.com>
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Acked-by: Rafael Antognolli <rafael.antognolli@intel.com>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/20190305124827.23446-1-michal.winiarski@intel.com