st/va: use drm render node for wayland display type

With xwayland, vainfo use VA_DISPLAY_WAYLAND as default and it fails
and fails when specify display with  `vainfo --display wayland`.
In fact wayland support for libva uses drm path to connect device,
and should use drm pipe loader to create screen.

Signed-off-by: Leo Liu <leo.liu@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>