score: select generic atomic64_t support

It's required for the core fs/namespace.c and many other basic features.

Signed-off-by: Fengguang Wu <fengguang.wu@intel.com>
Acked-by: Lennox Wu <lennox.wu@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>