perf_event: remove context "cookie" field
perf_event: remove context "cookie" field

It was a bit of overkill, we just need an initialized field.
Also revamp how context and control are initialized.

arm-hpc/papi,pyrovski/papi,pyrovski/papi,pyrovski/papi,pyrovski/papi,arm-hpc/papi,arm-hpc/papi,pyrovski/papi,arm-hpc/papi,arm-hpc/papi,pyrovski/papi,arm-hpc/papi,arm-hpc/papi,pyrovski/papi,pyrovski/papi