fs/dirent: add d_ino member to struct dirent

Add the POSIX d_ino (file serial number) member to struct dirent and
populate it on every readdir() path, so portable callers (e.g. scp in
dropbear) that read dp->d_ino observe a meaningful, non-zero inode
number:

  - include/dirent.h: declare d_ino in struct dirent and drop the
    outdated comment claiming the field is unimplemented.
  - include/nuttx/fs/hostfs.h: add d_ino to struct nuttx_dirent_s so
    the hostfs ABI can carry the inode number across the VFS boundary.
  - arch/sim/src/sim/posix/sim_hostfs.c: forward the host's
    ent->d_ino into entry->d_ino.
  - fs/vfs/fs_dir.c (read_pseudodir): copy the in-memory inode's
    i_ino into entry->d_ino for the pseudo filesystem.
  - fs/yaffs/yaffs_vfs.c: forward yaffs's dirent->d_ino into
    entry->d_ino.
  - fs/rpmsgfs: extend struct rpmsgfs_readdir_s with an 'ino' field
    and propagate it across the RPC in both rpmsgfs_server (fills it
    from the underlying entry) and rpmsgfs_client (writes it back to
    the caller's nuttx_dirent_s).

Signed-off-by: Xiang Xiao <xiaoxiang@xiaomi.com>

include/dirent.h

@@ -107,11 +107,12 @@
  * of char containing at least {NAME_MAX} plus one elements.
  *
  * POSIX also requires the field d_ino (type ino_t) that provides the file
- * serial number.  This functionality is not implemented in NuttX.
+ * serial number.
  */
 
 struct dirent
 {
+  ino_t    d_ino;                 /* File serial number */
   uint8_t  d_type;                /* Type of file */
   char     d_name[NAME_MAX + 1];  /* File name */
 };

include/nuttx/fs/hostfs.h

@@ -150,6 +150,7 @@ struct nuttx_timespec
 
 struct nuttx_dirent_s
 {
+  nuttx_ino_t  d_ino;
   uint8_t      d_type;                      /* type of file */
   char         d_name[CONFIG_NAME_MAX + 1]; /* filename */
 };