radv: fix occlusion queries on VegaM

The number of render backends is 16 but the enabled mask is 0xaaaa.

As noticed by Bas, allowing disabled render backends might break
the OCCLUSION_QUERY packet. We don't use it yet but keep this in
mind.

This fixes dEQP-VK.query_pool.* and dEQP-VK.multiview.*.

Cc: 19.0 19.1 <mesa-stable@lists.freedesktop.org>
Signed-off-by: Samuel Pitoiset <samuel.pitoiset@gmail.com>
Reviewed-By: Bas Nieuwenhuizen <bas@basnieuwenhuizen.nl>
(cherry picked from commit 2ef9d273)