devtools: accept experimental symbol promotion

devtools: accept experimental symbol promotion

Currently, when symbols get promoted from the EXPERIMENTAL section to a
stable ABI section, the script complains they should go to the
EXPERIMENTAL section.

Example:
ERROR: symbol rte_devargs_add is added in the DPDK_19.05 section, but is
expected to be added in the EXPERIMENTAL section of the version map

This is legit.
Moving from a stable ABI to another is also allowed, but must have gone
through the proper process.

Fixes: 4bec48184e33 ("devtools: add checks for ABI symbol addition")
Cc: stable@dpdk.org
Signed-off-by: David Marchand <david.marchand@redhat.com>
Acked-by: Neil Horman <nhorman@tuxdriver.com>