eal: check coremask against detected lcores

eal: check coremask against detected lcores

lcores that are set in coremask should be checked against lcores detected on
system. This way, we won't need to check them later.

Besides, if specifying an unavailable lcore, we currently panic in
eal_thread_loop() because pthread_setaffinity_np fails.
So this check will return an error with a more explicit message in
eal_parse_coremask().

"EAL: pthread_setaffinity_np failed
 PANIC in eal_thread_loop():
 cannot set affinity"

becomes :

"EAL: lcore 4 unavailable
 EAL: invalid coremask"

Signed-off-by: David Marchand <david.marchand@6wind.com>
Acked-by: Neil Horman <nhorman@tuxdriver.com>