winsys/amdgpu: Set RADEON_FLAG_32BIT again
Avoids hang running
rendercheck -t cacomposite -f a8r8g8b8"
via glamor on Navi 14.
Closes: #7167 (closed) Fixes: 7833c513 ("winsys/amdgpu: use cached GTT for command buffers and don't set the 32BIT flag")