drm/gm107/gr: bump attrib cb size quite a bit

When initially looking at traces, missed the fact the binary driver was
using large pages.

Fixes page faults when launching geometry shaders.

Signed-off-by: Ben Skeggs <bskeggs@redhat.com>

diff --cc drivers/gpu/drm/nouveau/core/engine/graph/ctxgm107.c
Simple merge