drm/xe/migrate: Remove unneeded emit_pte() when copying CCS only

In xe_migrate_copy(), when copy_only_ccs is true, we only need two
emit_pte() calls one for the BO and one for the raw CCS storage.
However, the current implementation issues three emit_pte() calls,
resulting in an unnecessary PTE programming job.

This fix removes the redundant emit_pte() call to avoid programming
the same PTEs twice and reducing overhead during CCS-only migration.

v2: Preserve correct behavior on DG2, which requires both CCS and
page copies.

Signed-off-by: Sanjay Yadav <sanjay.kumar.yadav@intel.com>
Suggested-by: Matthew Auld <matthew.auld@intel.com>
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Signed-off-by: Matthew Auld <matthew.auld@intel.com>
Link: https://lore.kernel.org/r/20250904161423.2448727-1-sanjay.kumar.yadav@intel.com