arm64/perf: Update struct pmu_hw_events for BRBE

A single perf event instance BRBE related contexts and data will be tracked
in struct pmu_hw_events. Hence update the structure to accommodate required
details related to BRBE.

Cc: Will Deacon <will@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: linux-arm-kernel@lists.infradead.org
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.com>