x32: update io_{setup,submit} syscalls

Starting in 3.16, these two syscalls have gotten their own entry
point for x32.  See linux 7fd44dacdd803c0bbf38bf478d51d280902bb0f1.

* linux/x32/syscallent.h: Change existing io_{setup,submit} to 64bit,
and add new entry points for x32 specifically.