include: prefer alsa/asoundlib.h for apps, dependency cleanups

Fixes several issues with header files:

- prefer alsa/asoundlib.h file for the alsa-lib core functionalities
  (use #warning to inform current and future developers, do the job)
- include alsa/asoundlib.h in headers for external plugins by default
- pcm_external.h: dependencies cleanup
- as benefit, the parsers in IDEs should get all information for individial
  header files (see PR#435)

This change was mainly tergetted to fix errors caused by wrong include order
(like for endianness detection, missing typedefs etc.).

Closes: https://github.com/alsa-project/alsa-lib/issues/431
Link: https://github.com/alsa-project/alsa-lib/pull/435
Signed-off-by: Jaroslav Kysela <perex@perex.cz>

include/local.h

@@ -30,6 +30,9 @@
 #include <string.h>
 #include <fcntl.h>
 #include <assert.h>
+#include <stdint.h>
+/* for timeval and timespec */
+#include <time.h>
 #ifdef HAVE_ENDIAN_H
 #include <endian.h>
 #elif defined(HAVE_SYS_ENDIAN_H)
@@ -187,6 +190,7 @@
 #include "hwdep.h"
 #include "control.h"
 #include "mixer.h"
+#include "ump_msg.h"
 #include "seq_event.h"
 #include "seq.h"