audit: inline audit_syscall_entry to reduce burden on archs

Every arch calls:

if (unlikely(current->audit_context))
	audit_syscall_entry()

which requires knowledge about audit (the existance of audit_context) in
the arch code.  Just do it all in static inline in audit.h so that arch's
can remain blissfully ignorant.

Signed-off-by: Eric Paris <eparis@redhat.com>
diff --git a/arch/xtensa/kernel/ptrace.c b/arch/xtensa/kernel/ptrace.c
index a0d042a..2dff698 100644
--- a/arch/xtensa/kernel/ptrace.c
+++ b/arch/xtensa/kernel/ptrace.c
@@ -334,8 +334,7 @@
 		do_syscall_trace();
 
 #if 0
-	if (unlikely(current->audit_context))
-		audit_syscall_entry(current, AUDIT_ARCH_XTENSA..);
+	audit_syscall_entry(current, AUDIT_ARCH_XTENSA..);
 #endif
 }