qemu-char: cleanup HAVE_CHARDEV_* Move the #ifdef up into qmp_chardev_add, and avoid duplicating the code that reports unavailable backends. Split HAVE_CHARDEV_TTY into HAVE_CHARDEV_SERIAL and HAVE_CHARDEV_PTY. Reviewed-by: Eric Blake <eblake@redhat.com> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>