KVM: arm64: PMU: Distinguish between 64bit counter and 64bit overflow

The PMU architecture makes a subtle difference between a 64bit
counter and a counter that has a 64bit overflow. This is for example
the case of the cycle counter, which can generate an overflow on
a 32bit boundary if PMCR_EL0.LC==0 despite the accumulation being
done on 64 bits.

Use this distinction in the few cases where it matters in the code,
as we will reuse this with PMUv3p5 long counters.

Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20221113163832.3154370-5-maz@kernel.org