nimble/host: Add some missing includes

Some of missing includes were implicitly added via other files and cause
problems when porting on different platforms.

nimble/host/services/bleuart/src/bleuart.c

@@ -20,6 +20,7 @@
 #include <assert.h>
 #include <stdio.h>
 #include <string.h>
+#include <stdlib.h>
 
 #include "sysinit/sysinit.h"
 #include "host/ble_hs.h"

nimble/host/src/ble_att_priv.h

@@ -22,6 +22,7 @@
 
 #include <inttypes.h>
 #include "stats/stats.h"
+#include "os/os_time.h"
 #include "os/queue.h"
 #include "host/ble_att.h"
 #include "host/ble_uuid.h"

nimble/host/src/ble_att_svr.c

@@ -17,6 +17,7 @@
  * under the License.
  */
 
+#include <stdlib.h>
 #include <string.h>
 #include <errno.h>
 #include "os/os.h"

nimble/host/src/ble_gatts.c

@@ -18,6 +18,7 @@
  */
 
 #include <stddef.h>
+#include <stdlib.h>
 #include <string.h>
 #include "nimble/ble.h"
 #include "host/ble_uuid.h"