etnaviv: fix gbm_bo_get_handle_for_plane for multiplanar images

etnaviv: fix gbm_bo_get_handle_for_plane for multiplanar images

Implement resource_get_param for PIPE_RESOURCE_PARAM_NPLANES and fix
resource_get_handle to walk to the correct linked resource for
multiplanar images, allowing gbm_bo_get_handle_for_plane to be called
with plane > 0.

This fixes an assert that is triggered when a wayland client tries
to send weston an NV12 dmabuf, for example:

  weston: .../mesa/src/gbm/backends/dri/gbm_dri.c:752: gbm_dri_bo_get_handle_for_plane: Assertion `plane == 0' failed.

Fixes: 788f6dc85781 ('Revert "gallium/dri: fix dri2_from_planar for multiplanar images"')
Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>
Reviewed-by: Christian Gmeiner <christian.gmeiner@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/12037>