perf: xgene: Add support for SoC PMU version 3

This patch adds support for SoC-wide (AKA uncore) Performance Monitoring
Unit version 3.

It can support up to
 - 2 IOB PMU instances
 - 8 L3C PMU instances
 - 2 MCB PMU instances
 - 8 MCU PMU instances
and these PMUs support 64 bit counter
Signed-off-by: NHoan Tran <hotran@apm.com>
[Mark: stop counters in _xgene_pmu_isr()]
Signed-off-by: NMark Rutland <mark.rutland@arm.com>
[will: make xgene_pmu_v3_ops static]
Signed-off-by: NWill Deacon <will.deacon@arm.com>