radv: Disallow indirect outputs for GS on GFX9 as well.

Since it also uses the output vector before writing to memory.

Fixes: e38685cc 'Revert "radv: disable support for VEGA for now."'
Reviewed-by: Dave Airlie <airlied@redhat.com>
Reviewed-by: Timothy Arceri <tarceri@itsqueeze.com>
(cherry picked from commit c07d719e)
[Bas Nieuwenhuizen: resolve conflicts]

Conflicts:
        src/amd/vulkan/radv_shader.c