bus: ARM CCN PMU driver

Driver providing perf backend for ARM Cache Coherent Network
interconnect. Supports counting all hardware events and crosspoint
watchpoints.

Currently works with CCN-504 only, although there should be
no changes required for CCN-508 (just impossible to test it now).

Signed-off-by: Pawel Moll <pawel.moll@arm.com>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>