drm/xe/selftests: make eviction test tile centric

The concern here is that we may have platforms with dedicated media GT,
and we anyway allocate the object on the tile, which just means running
the same test twice (i.e primary vs media GT).

Signed-off-by: Matthew Auld <matthew.auld@intel.com>
Cc: Nirmoy Das <nirmoy.das@intel.com>
Reviewed-by: Nirmoy Das <nirmoy.das@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>