drm/amdkfd: debug message to count successfully migrated pages

drm/amdkfd: debug message to count successfully migrated pages

Not all migrate.cpages returned from migrate_vma_setup can be migrated,
for example non anonymous page, or out of device memory. So after
migrate_vma_pages returns, add debug message to count pages are
successfully migrated which has MIGRATE_PFN_VALID and
MIGRATE_PFN_MIGRATE flag set.

Signed-off-by: Philip Yang <Philip.Yang@amd.com>
Reviewed-by: Felix Kuehling <Felix.Kuehling@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>