drm/nouveau: finalise nvkm namespace switch (no binary change)

The namespace of NVKM is being changed to nvkm_ instead of nouveau_,
which will be used for the DRM part of the driver.  This is being
done in order to make it very clear as to what part of the driver a
given symbol belongs to, and as a minor step towards splitting the
DRM driver out to be able to stand on its own (for virt).

Because there's already a large amount of churn here anyway, this is
as good a time as any to also switch to NVIDIA's device and chipset
naming to ease collaboration with them.

A comparison of objdump disassemblies proves no code changes.

Signed-off-by: Ben Skeggs <bskeggs@redhat.com>

drivers/gpu/drm/nouveau/nouveau_encoder.h

@@ -34,14 +34,14 @@
 
 #define NV_DPMS_CLEARED 0x80
 
-struct nouveau_i2c_port;
+struct nvkm_i2c_port;
 
 struct nouveau_encoder {
 	struct drm_encoder_slave base;
 
 	struct dcb_output *dcb;
 	int or;
-	struct nouveau_i2c_port *i2c;
+	struct nvkm_i2c_port *i2c;
 
 	/* different to drm_encoder.crtc, this reflects what's
 	 * actually programmed on the hw, not the proposed crtc */