clients/simple-dmabuf-feedback: Add fallback print method for unknown formats

Using pixel_format_get_info() can result in formats being reported as UNKNOWN when used on compositors other than Weston.

As weston-simple-dmabuf-feedback somewhat succeeds wayland-info as tool for zwp_linux_dmabuf_v1 debugging from version 4 on, copy the approach from the later for these cases.