perf/arm-cmn: Optimise DTC counter accesses

perf/arm-cmn: Optimise DTC counter accesses

In cases where we do know which DTC domain a node belongs to, we can
skip initialising or reading the global count in DTCs where we know
it won't change. The machinery to achieve that is mostly in place
already, so finish hooking it up by converting the vestigial domain
tracking to propagate suitable bitmaps all the way through to events.

Note that this does not allow allocating such an unused counter to a
different event on that DTC, because that is a flippin' nightmare.

Signed-off-by: Robin Murphy <robin.murphy@arm.com>
Link: https://lore.kernel.org/r/51d930fd945ef51c81f5889ccca055c302b0a1d0.1638530442.git.robin.murphy@arm.com
Signed-off-by: Will Deacon <will@kernel.org>