x86: undo part of "refine link time stub area related assertion"

x86: undo part of "refine link time stub area related assertion"

The original check was not too strict: While we don't use one page of
memory per CPU, we do use ons page of VA space per CPU. It is the
latter which matters here.

Undo that part of the change, but leave everything else in place.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Andrew Cooper <andrew.cooper3@citrix.com>