bus: arm-ccn: Fix spurious warning message

Because CCN's cycle counter always runs, it will generate
an interrupt on overflow even if the relevant perf event
was not requested, causing a spurious warning message.

Fixed now by warning on only normal counter unwanted
overflows. Also cleaning the overflow mask at init now,
not to warn on event previously requested by firmware.

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