Add GPU work metrics processing

Add gpu_work eBPF program that defines the format of and processes the
power/gpu_work_period tracepoint.

Add code to gpuservice that attaches the eBPF program and reports the
GPU time in frequency state stats via `dumpsys gpu --gpuwork`.

Bug: b/213577594
Change-Id: I2774909e8a375a8b20e6fb55f8069ecdbe650ef2