eal: add wrapper for C11 atomic thread fence

eal: add wrapper for C11 atomic thread fence

Provide a wrapper for __atomic_thread_fence builtins to support
optimized code for __ATOMIC_SEQ_CST memory order for x86 platforms.

Suggested-by: Honnappa Nagarahalli <honnappa.nagarahalli@arm.com>
Signed-off-by: Phil Yang <phil.yang@arm.com>
Reviewed-by: Ola Liljedahl <ola.liljedahl@arm.com>
Acked-by: Konstantin Ananyev <konstantin.ananyev@intel.com>