[Nouveau] VBO flush method on Maxwell (GM107)

[Ilia Mirkin]

Hello,

The method we previously used on Fermi and Kepler (0x142c) to flush
the VBO cache before draw appears to be gone on Maxwell. Is there a
replacement method we should use?

(Or perhaps that method was never meant for VBO cache flush and
instead flushed something related to the vertex quarantine area
defined by 0x17bc/0x17c0/0x17c4, which in turn is gone on Maxwell?)

Thanks for any light you might shed on this. We're seeing occasional
rendering issues in Xonotic, and think this could contribute to the
cause.

Cheers,

  -ilia