freedreno/rnn: update schema for 'pos'

Ideally we'd like to express that *either* 'high' + 'low' OR 'pos' is
required, but it doesn't appear that this is possible.  But the rnn
parsing code should still enforce this.

Signed-off-by: Rob Clark <robdclark@chromium.org>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/6107>
1 file changed