drm/i915/gt: Add selftests for TLB invalidation

drm/i915/gt: Add selftests for TLB invalidation

Check that we invalidate the TLB cache, the updated physical addresses
are immediately visible to the HW, and there is no retention of the old
physical address for concurrent HW access.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
[ahajda: adjust to upstream driver, v2+]
Signed-off-by: Andrzej Hajda <andrzej.hajda@intel.com>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
[tursulin: Small indentation fix.]
Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230130165058.1647414-1-andrzej.hajda@intel.com