[Nouveau] SERIALIZE command

[Shinpei KATO]

This is a follow-up.

> The command is known to work on all NV50 objects. Pre-NV50, only a few objects
> support it, and I'm not fully certain if the address is 0x108 or 0x110...
> it's
> 0x110 at least on the NV40 3d object.

I tried inserting the 0x110 commands with NvSubM2MF (subc=0), MvSubSw (subc=1), NvSub2D (subc=2), NvSubGdiRect (subc=3), NvSubImageBlit (subc=4).
As a result, I got the PFIFO_CACHE_ERROR interrupts, with respect to those with NvSubSw and NvSubImageBlit.
I am really not certain what PFIFO_CACHE_ERROR indicates, but seems they do not work correctly?
Well, those with NvSubM2MF, NvSub2D and NvSubGdiRect are still very helpful though.

Thanks,
- Shinpei