turnip: Always use GMEM for feedback loops in autotuner

For ordinary feedback loops GMEM is a lot faster than sysmem since
we don't set SINGLE_PRIM mode.

For feedback loops with ordered rasterization GMEM should also be
faster.

Signed-off-by: Danylo Piliaiev <dpiliaiev@igalia.com>
Part-of: <!15106>