drm/amdgpu: Warn and update pin_size values when destroying a pinned BO

This shouldn't happen, but if it does, we'll get a backtrace of the
caller, and update the pin_size values as needed.

v2:
* Check bo->pin_count instead of placement flags (Christian König)

Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Michel Dänzer <michel.daenzer@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>