FROMGIT: ARM: Remove custom IRQ stat accounting

Let's switch the arm code to the core accounting, which already
does everything we need.

Reviewed-by: Valentin Schneider <valentin.schneider@arm.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>

Bug: 140053385
(cherry picked from commit 5ebf353a
 https://git.kernel.org/pub/scm/linux/kernel/git/maz/arm-platforms.git

 irq/ipi-as-irq)
Change-Id: I8c6f00111924e491a8f384e9c194ab223d5dabc2
Signed-off-by: Eric Biggers <ebiggers@google.com>