[ALSA] Fix control/status mmap with shared PCM substream

The flag to avoid 32bit-incompatible mmap for control/status records
should be outside the pcm substream instance since a substream can be
shared among multiple opens.  Now it's flagged in pcm_file list that
is directly assigned to file->private_data.
Also, removed snd_pcm_add_file() and remove_file() functions and
substream.files field that are not really used in the code.

Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Jaroslav Kysela <perex@suse.cz>
diff --git a/sound/core/pcm_compat.c b/sound/core/pcm_compat.c
index 2b8aab6..2b53979 100644
--- a/sound/core/pcm_compat.c
+++ b/sound/core/pcm_compat.c
@@ -478,7 +478,7 @@
 	 * mmap of PCM status/control records because of the size
 	 * incompatibility.
 	 */
-	substream->no_mmap_ctrl = 1;
+	pcm_file->no_compat_mmap = 1;
 
 	switch (cmd) {
 	case SNDRV_PCM_IOCTL_PVERSION: