panfrost: Don't round up Midgard polygon list BOs

panfrost: Don't round up Midgard polygon list BOs

Rounding up the polygon list BO can waste large amounts of memory. In a common
case I observed, it rounded up 11MB to 16MB, wasting 5MB. That adds up quickly
across processes, especially on the 2GB machines.

This only applies to Midgard. On Bifrost and newer, the driver does not
explicitly allocate this data structure. Cc stable because this rounding is
incorrect and the increase in RAM usage can cause real problems (especially
given how slow the shrinker is).

Signed-off-by: Alyssa Rosenzweig <alyssa@collabora.com>
Cc: mesa-stable
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/21831>