eal: mark version parts API as experimental

eal: mark version parts API as experimental

Some functions were introduced in DPDK 21.05 to query the version parts
(prefix, year, month, minor, suffix, release) at runtime.
Per guidelines, these new public functions must be marked with
__rte_experimental and ABI versioned as EXPERIMENTAL.

Fixes: 5b637a848195 ("eal: fix querying DPDK version at runtime")
Cc: stable@dpdk.org
Suggested-by: David Marchand <david.marchand@redhat.com>
Signed-off-by: Thomas Monjalon <thomas@monjalon.net>
Acked-by: Bruce Richardson <bruce.richardson@intel.com>