x86: signal: cosmetic unification of __setup_sigframe() and __setup_rt_sigframe()

Impact: cleanup

Add #ifdef directive to unify __setup_sigframe() and __setup_rt_sigframe().
Move them after {setup|restore}_sigcontext() declaration.

Signed-off-by: Hiroshi Shimamoto <h-shimamoto@ct.jp.nec.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>