drm/nouveau/ttm: plumb ctx through move functions.

This just uses the ctx instead of passing bools and recreating it.

Acked-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200923030454.362731-5-airlied@gmail.com