drivers: perf: arm_pmu: Add infrastructure for branch stack sampling

In order to support the Branch Record Buffer Extension (BRBE), we need to
extend the arm_pmu framework with some basic infrastructure for the branch
stack sampling which arm_pmu drivers can opt-in using a new feature flag
called 'has_branch_stack'. Subsequent patches will use this to add support
for BRBE in the PMUv3 driver.

Branch stack sampling support i.e capturing branch records during execution
in core perf, rides along with normal HW events being scheduled on the PMU.
This prepares ARMV8 PMU framework for branch stack support on relevant PMUs
with required HW implementation.

With BRBE, the hardware records branches into a hardware FIFO, which will
be sampled by software when perf events overflow. A task may be context-
switched an arbitrary number of times between overflows, and to avoid
losing samples we need to save the current records when a task is context-
switched out. To do these we'll need to use the pmu::sched_task() callback,
and we'll also need to allocate some per-task storage space via event flag
PERF_ATTACH_TASK_DATA.

Cc: Catalin Marinas <catalin.marinas@arm.com>
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>
----
Changes in V17:

- ARM PMUV3 changes have been moved into the BRBE driver patch instead
- Moved down branch_stack_add() in armpmu_add() after event's basic checks
- Added new callbacks in struct arm_pmu e.g branch_stack_[init|add|del]()
- Renamed struct arm_pmu callback branch_reset() as branch_stack_reset()
- Dropped the comment in armpmu_event_init()
- Renamed 'pmu_hw_events' elements from 'brbe_' to more generic 'branch_'