[PATCH] powerpc: Add accounting for Doorbell interrupts

[Ian Munsie]

Excerpts from Michael Ellerman's message of 2013-03-22 15:18:03 +1100:
> On Wed, Mar 20, 2013 at 06:42:12PM +1100, Ian Munsie wrote:
> > From: Ian Munsie <imunsie at au1.ibm.com>
> > 
> > This patch adds a new line to /proc/interrupts to account for the
> > doorbell interrupts that each hardware thread has received. The total
> > interrupt count in /proc/stat will now also include doorbells.
> 
> Should it be inside CONFIG_PPC_DOORBELL ?

The doorbell line will only show up in /proc/interrupt if CPU_FTR_DBELL
is set and the total interrupt count in /proc/stat will be unaffected
if we don't have doorbells (+ 0 doorbells). It still builds fine without
CONFIG_PPC_DOORBELL.

Adding #ifdefs would save one per cpu integer in irq_stat. I can throw
together a v2 patch with them in place.

Cheers,
-Ian