eal: use C11 atomics for initialization check

eal: use C11 atomics for initialization check

Since rte_atomicXX APIs are not allowed to be used, use C11 builtins to
check if EAL is already initialized.

Signed-off-by: Phil Yang <phil.yang@arm.com>
Reviewed-by: Honnappa Nagarahalli <honnappa.nagarahalli@arm.com>
Reviewed-by: Ruifeng Wang <ruifeng.wang@arm.com>