If the user has requested a counting threshold for the CPU cycles event,
then the fixed cycle counter can't be assigned as it lacks threshold
support. Currently, the thresholds will work or not randomly depending
on which counter the event is assigned.

While using thresholds for CPU cycles doesn't make much sense, it can be
useful for testing purposes.

Fixes: 816c2675 ("arm64: perf: Add support for event counting threshold")
Signed-off-by: Rob Herring (Arm) <robh@kernel.org>
Acked-by: Mark Rutland <mark.rutland@arm.com>
Link: https://lore.kernel.org/r/20240626-arm-pmu-3-9-icntr-v2-1-c9784b4f4065@kernel.orgSigned-off-by: Will Deacon <will@kernel.org>