CLEANUP: include: make atomic.h part of the base API

Atomic ops are used about everywhere, let's make them part of the base
API by including atomic.h in api.h.
diff --git a/include/haproxy/activity.h b/include/haproxy/activity.h
index 452e5f8..7b68530 100644
--- a/include/haproxy/activity.h
+++ b/include/haproxy/activity.h
@@ -22,7 +22,6 @@
 #ifndef _HAPROXY_ACTIVITY_H
 #define _HAPROXY_ACTIVITY_H
 
-#include <haproxy/atomic.h>
 #include <haproxy/api.h>
 #include <haproxy/time.h>
 #include <haproxy/activity-t.h>
diff --git a/include/haproxy/api.h b/include/haproxy/api.h
index f32050d..dd8b02a 100644
--- a/include/haproxy/api.h
+++ b/include/haproxy/api.h
@@ -30,6 +30,7 @@
 #ifndef _HAPROXY_BASE_H
 #define _HAPROXY_BASE_H
 
+#include <haproxy/atomic.h>
 #include <haproxy/bug.h>
 #include <haproxy/initcall.h>
 #include <haproxy/api-t.h>
diff --git a/include/haproxy/freq_ctr.h b/include/haproxy/freq_ctr.h
index ba9de69..ce6fb95 100644
--- a/include/haproxy/freq_ctr.h
+++ b/include/haproxy/freq_ctr.h
@@ -22,7 +22,6 @@
 #ifndef _HAPROXY_FREQ_CTR_H
 #define _HAPROXY_FREQ_CTR_H
 
-#include <haproxy/atomic.h>
 #include <haproxy/api.h>
 #include <haproxy/freq_ctr-t.h>
 #include <haproxy/intops.h>
diff --git a/include/haproxy/port_range.h b/include/haproxy/port_range.h
index be0160b..8e7a937 100644
--- a/include/haproxy/port_range.h
+++ b/include/haproxy/port_range.h
@@ -23,7 +23,6 @@
 #define _HAPROXY_PORT_RANGE_H
 
 #include <stdlib.h>
-#include <haproxy/atomic.h>
 #include <haproxy/api.h>
 #include <haproxy/port_range-t.h>
 
diff --git a/include/haproxy/thread.h b/include/haproxy/thread.h
index 1afd958..6520b77 100644
--- a/include/haproxy/thread.h
+++ b/include/haproxy/thread.h
@@ -29,7 +29,6 @@
 #include <sched.h>
 #endif
 
-#include <haproxy/atomic.h>
 #include <haproxy/api.h>
 #include <haproxy/thread-t.h>
 
diff --git a/include/haproxy/xref.h b/include/haproxy/xref.h
index e766385..42eed58 100644
--- a/include/haproxy/xref.h
+++ b/include/haproxy/xref.h
@@ -28,7 +28,6 @@
 #ifndef __HAPROXY_XREF_H__
 #define __HAPROXY_XREF_H__
 
-#include <haproxy/atomic.h>
 #include <haproxy/xref-t.h>
 
 /* xref is used to create relation between two elements.