drm/nouveau/kms/nv50-: Move hard-coded object handles into header

While most of the functionality on Nvidia GPUs doesn't require using an
explicit handle instead of the main VRAM handle + offset, there are a
couple of places that do require explicit handles, such as CRC
functionality. Since this means we're about to add another
nouveau-chosen handle, let's just go ahead and move any hard-coded
handles into a single header. This is just to keep things slightly
organized, and to make it a little bit easier if we need to add more
handles in the future.

This patch should contain no functional changes.

Changes since v3:
* Correct SPDX license identifier (checkpatch)

Signed-off-by: Lyude Paul <lyude@redhat.com>
Reviewed-by: Ben Skeggs <bskeggs@redhat.com>
Acked-by: Dave Airlie <airlied@gmail.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200627194657.156514-9-lyude@redhat.com