perf: arm_pmu: Kill last use of per-CPU cpu_armpmu pointer

perf: arm_pmu: Kill last use of per-CPU cpu_armpmu pointer

Having removed the use of the cpu_armpmu per-CPU variable from the
interrupt handling, the only user left is the BRBE scheduler hook.

It is easy to drop the use of this variable by following the pointer to the
generic PMU structure, and get the arm_pmu structure from there.

Perform the conversion and kill cpu_armpmu altogether.

Suggested-by: Will Deacon <will@kernel.org>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Will Deacon <will@kernel.org>
Link: https://patch.msgid.link/20251020122944.3074811-27-maz@kernel.org