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 branch
stack sampling which arm_pmu drivers can opt-in to using. Subsequent
patches will use this to add support for BRBE in the PMUv3 driver.

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>
----

 drivers/perf/arm_pmu.c       | 25 ++++++++++++++++++++++---
 include/linux/perf/arm_pmu.h | 32 +++++++++++++++++++++++++++++++-
 2 files changed, 53 insertions(+), 4 deletions(-)