nouveau: Various internal and external API changes

1. DRM_NOUVEAU_GPUOBJ_FREE
	Used to free GPU objects.  The obvious usage case is for Gr objects,
	but notifiers can also be destroyed in the same way.

	GPU objects gain a destructor method and private data fields with
	this change, so other specialised cases (like notifiers) can be
	implemented on top of gpuobjs.

2. DRM_NOUVEAU_CHANNEL_FREE

3. DRM_NOUVEAU_CARD_INIT
	Ideally we'd do init during module load, but this isn't currently
	possible.  Doing init during firstopen() is bad as X has a love of
	opening/closing the DRM many times during startup.  Once the
	modesetting-101 branch is merged this can go away.

	IRQs are enabled in nouveau_card_init() now, rather than having the
	X server call drmCtlInstHandler().  We'll need this for when we give
	the kernel module its own channel.

4. DRM_NOUVEAU_GETPARAM
	Add CHIPSET_ID value, which will return the chipset id derived
	from NV_PMC_BOOT_0.

4. Use list_* in a few places, rather than home-brewed stuff.