drivers: perf: arm_pmuv3: Enable branch stack sampling framework

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.

ARMV8 PMU hardware support for branch stack sampling is indicated via a new
feature flag called 'has_branch_stack' that can be ascertained via probing.
This modifies current gate in armpmu_event_init() which blocks branch stack
sampling based perf events unconditionally. Instead allows such perf events
getting initialized on supporting PMU hardware.

Branch stack sampling is enabled and disabled along with regular PMU events
. This adds required function callbacks in armv8pmu_branch_xxx() format, to
drive the PMU branch stack hardware when supported. This also adds fallback
stub definitions for these callbacks for PMUs which would not have required
support.

If a task gets scheduled out, the current branch records get saved in the
task's context data, which can be later used to fill in the records upon an
event overflow. Hence, we enable PERF_ATTACH_TASK_DATA (event->attach_state
based flag) for branch stack requesting perf events. But this also requires
adding support for pmu::sched_task() callback to arm_pmu.

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>