This probably isn't the ideal fix, but we ended up using chids
sparsely, and lots of things rely on indexing into the full range,
so just allocate the full range up front.

The GSP code fixes 8 channels into a userd page, but we end up using
a single userd page per channel so end up sparsely using the range.

Fixes a few crashes seen with multiple channels.

Link: https://gitlab.freedesktop.org/drm/nouveau/-/issues/277


Signed-off-by: Dave Airlie <airlied@redhat.com>
Signed-off-by: Danilo Krummrich <dakr@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20231121201109.2988516-1-airlied@gmail.com