drm/vc4: Fix ioctl permissions for render nodes.

Contrary to other flags to DRM_IOCTL_DEF_DRV(), which restrict usage,
the flag for render node is an enabler (the IOCTL can't be used from
render node if it's not present).  So DRM_RENDER_ALLOW needs to be
added to all the flags that were previously 0.

Signed-off-by: Herve Jourdain <herve.jourdain@neuf.fr>
Reviewed-by: Eric Anholt <eric@anholt.net>
Fixes: 0cd3e274 ("drm/vc4: Add missing render node support")