Improve DLB+PME tuning with GPUs

Improve DLB+PME tuning with GPUs

With GPUs and the DD DLB can quickly limit the PME load balancing
room too much. In such cases (and only with DLB=auto) we now first
do PME load balancing without DLB and then, if DLB gets turned on,
a second round of PME load balancing.

Also fixed that when DLB limited the tuning, the fastest choice was
reset, which would often lead to stronger limitations.

Change-Id: I0087e6b8512d5574d8d0fa2db82e6e38279a82f1