mali_kbase: dvfs: add min gpu level for compute.

Adds a DTBO entry that can be used to set the minimum dvfs OPP when
compute contexts are detected running. This effectively uses compute as
a proxy signal that there are realtime workloads present

Bug: 178234323
Test: tflite does up gpu frequency.
Test: UI does not up gpu frequency.
Change-Id: Iea8e03e242cee9451ef8500df060b53607789f2b