x86/apic: Provide apic_ack_irq()

apic_ack_edge() is explicitely for handling interrupt affinity cleanup when
interrupt remapping is not available or disable.

Remapped interrupts and also some of the platform specific special
interrupts, e.g. UV, invoke ack_APIC_irq() directly.

To address the issue of failing an affinity update with -EBUSY the delayed
affinity mechanism can be reused, but ack_APIC_irq() does not handle
that. Adding this to ack_APIC_irq() is not possible, because that function
is also used for exceptions and directly handled interrupts like IPIs.

Create a new function, which just contains the conditional invocation of
irq_move_irq() and the final ack_APIC_irq().

Reuse the new function in apic_ack_edge().

Preparatory change for the real fix.

Fixes: dccfe314 ("x86/vector: Simplify vector move cleanup")
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Song Liu <songliubraving@fb.com>
Cc: Joerg Roedel <jroedel@suse.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Song Liu <liu.song.a23@gmail.com>
Cc: Dmitry Safonov <0x7f454c46@gmail.com>
Cc: stable@vger.kernel.org
Cc: Mike Travis <mike.travis@hpe.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Tariq Toukan <tariqt@mellanox.com>
Link: https://lkml.kernel.org/r/20180604162224.471925894@linutronix.de