drm/ttm: warn stricter about freeing pinned BOs

So far we only warned when the BOs where pinned and not idle.

Also warn if we see a pinned BO in general.

Signed-off-by: Christian König <christian.koenig@amd.com>
Acked-by: Leo Liu <leo.liu@amd.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210415084730.2057-3-christian.koenig@amd.com