consolidate declarations of k_sigaction

Only alpha and sparc are unusual - they have ka_restorer in it.
And nobody needs that exposed to userland.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

arch/sparc/include/asm/signal.h

@@ -21,10 +21,7 @@
  */
 #define SA_STATIC_ALLOC         0x8000
 
-struct k_sigaction {
-	struct			__new_sigaction sa;
-	void			__user *ka_restorer;
-};
+#define __ARCH_HAS_KA_RESTORER
 
 #endif /* !(__ASSEMBLY__) */
 #endif /* !(__SPARC_SIGNAL_H) */