drm/xe: handle TLB invalidations from CT fast-path

In various test cases that put the system under a heavy load, we can
sometimes see errors with missed TLB invalidations. In such cases we see
the interrupt arrive for the invalidation from the GuC, however the
actual processing of the completion is pushed onto a workqueue and
handled with all the other CT stuff, which might take longer than
expected. Since we expect TLB invalidations to complete within a
reasonable amount of time (at most ~250ms), and they do seem pretty
critical, allow handling directly from the CT fast-path.

v2 (José):
  - Actually use the correct spinlock/unlock_irq, since pending_lock is
    grabbed from IRQ.
v3:
  - Don't publish the TLB fence on the list until after we fully
    initialize it and successfully do the CT send. The list is now only
    protected by the spin_lock pending_lock and we can't hold that
    across the entire TLB send operation.
v4 (Matt Brost):
  - Be careful with racing against fast CT path writing the seqno,
    before we have actually published the fence.

References: #297
References: #320
References: #449


Signed-off-by: Matthew Auld <matthew.auld@intel.com>
Cc: Matthew Brost <matthew.brost@intel.com>
Cc: José Roberto de Souza <jose.souza@intel.com>
Reviewed-by: Matthew Brost <matthew.brost@intel.com>