Move GPU task assignment

Move GPU task assignment

This commit changes no functionality except that it does re-order some
log-file reporting, with GPU task assignment reporting now preceding
OpenMP and thread affinity reporting.

Now that there is multi-stage DD construction, the GPU task assignment
can be done between the stages. This will permit the construction of
GPU resources in time to build domain objects with GPU stream(s),
where appropriate.

Change-Id: I1734afa65ee5b54995ccf23a69ff25ec6587a019