perf/arm-cmn: Refactor node ID handling

perf/arm-cmn: Refactor node ID handling

Add a bit more abstraction for the places where we decompose node IDs.
This will help keep things nice and manageable when we come to add yet
more variables which affect the node ID format. Also use the opportunity
to move the rest of the low-level node management helpers back up to the
logical place they were meant to be - how they ended up buried right in
the middle of the event-related definitions is somewhat of a mystery...

Signed-off-by: Robin Murphy <robin.murphy@arm.com>
Link: https://lore.kernel.org/r/a2242a8c3c96056c13a04ae87bf2047e5e64d2d9.1638530442.git.robin.murphy@arm.com
Signed-off-by: Will Deacon <will@kernel.org>