dri / radeonsi: PIPE_BIND_DRI_PRIME related minor changes
cc @kwg: the first commit should fix the "PIPE_BIND_DRI_PRIME / __DRI_IMAGE_PRIME_LINEAR_BUFFER is a specific punchthrough that isn't even the case for many PRIME setup" issue you noticed.
(at least it's not dependent on draw->dri_screen_display_gpu
being set anymore)