[Nouveau] Interrupt setting

[Marcin Kościelnicki]

> The presence of some rendering artifacts casts some doubts on this,
> but the consensus is that it is more likely due to missing cache
> flushing or something else.

I cannot comment on pre-NV50, but on NV50 PGRAPH commands are asynchronous for 
sure. You can insert a PGRAPH command barrier by using method SERIALIZE 
[0x110]. No idea yet about PFIFO<->PGRAPH sync.

Marcin Kościelnicki