venus: raise the ring buffer size to 64KB

venus: raise the ring buffer size to 64KB

When the renderer supports largeRing, raise the ring buffer size to 64KB
and raise the direct submit threshold to 4KB.  The numbers are randomly
picked.

Signed-off-by: Chia-I Wu <olvaffe@gmail.com>
Reviewed-by: Yiwei Zhang <zzyiwei@chromium.org>
Reviewed-by: Ryan Neph <ryanneph@google.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/12568>