eal: register non-EAL threads as lcores

eal: register non-EAL threads as lcores

DPDK allows calling some part of its API from a non-EAL thread but this
has some limitations.
OVS (and other applications) has its own thread management but still
want to avoid such limitations by hacking RTE_PER_LCORE(_lcore_id) and
faking EAL threads potentially unknown of some DPDK component.

Introduce a new API to register non-EAL thread and associate them to a
free lcore with a new NON_EAL role.
This role denotes lcores that do not run DPDK mainloop and as such
prevents use of rte_eal_wait_lcore() and consorts.

Multiprocess is not supported as the need for cohabitation with this new
feature is unclear at the moment.

Signed-off-by: David Marchand <david.marchand@redhat.com>
Acked-by: Andrew Rybchenko <arybchenko@solarflare.com>
Acked-by: Thomas Monjalon <thomas@monjalon.net>
Acked-by: Konstantin Ananyev <konstantin.ananyev@intel.com>