perf: Retire PERF_PMU_CAP_NO_INTERRUPT

Now that we have a well-defined cap for sampling support, clean up the
remains of the mildly unintuitive and inconsistently-applied
PERF_PMU_CAP_NO_INTERRUPT. Not to mention the obvious redundancy of
some of these drivers still checking for sampling in event_init too.

Signed-off-by: Robin Murphy <robin.murphy@arm.com>