SPDX status with 20.2

Only a few places still need addressing

$ ./devtools/check-spdx-tag.sh -v
Files without SPDX License
--------------------------

Files with redundant license text
---------------------------------
app/test/test_timer_racecond.c
lib/librte_ethdev/rte_ethdev_pci.h
lib/librte_ethdev/rte_ethdev_vdev.h