Message type for path related calls.

Message type for path related calls.

 - Updated system calls VFS_ACCESS, VFS_CHDIR, VFS_CHMOD, VFS_CHROOT,
                        VFS_MKDIR, VFS_OPEN, VFS_RMDIR, VSF_UNLINK

 - Removed M3_STRING and M3_LONG_STRING, which are tied to a specific
   "generic" message, and replaced where needed with M_PATH_STRING_MAX,
   which is tied to the mess_lc_vfs_path message.

Change-Id: If287c74f5ece937b9431e5d95b5b58a3c83ebff1