drm/nouveau/therm: convert to new-style nvkm_subdev

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

drm/nouveau/therm: cosmetic changes

This is purely preparation for upcoming commits, there should be no
code changes here.

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

drm/nouveau/therm: namespace + nvidia gpu names (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>

drm/nouveau: remove symlinks, move core/ to nvkm/ (no code changes)

The symlinks were annoying some people, and they're not used anywhere
else in the kernel tree. The include directory structure has been
changed so that symlinks aren't needed anymore.

NVKM has been moved from core/ to nvkm/ to make it more obvious as to
what the directory is for, and as some minor prep for when NVKM gets
split out into its own module (virt) at a later date.

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