MIPS: Add hook to get C0 performance counter interrupt

The hardware perf event driver and oprofile interpret the global
cp0_perfcount_irq differently: in the hardware perf event driver
it is an offset from MIPS_CPU_IRQ_BASE and in oprofile it is the
actual IRQ number.  This still works most of the time since
MIPS_CPU_IRQ_BASE is usually 0, but is clearly wrong.  Since the
performance counter interrupt may vary from platform to platform
like the C0 timer interrupt, add the optional get_c0_perfcount_int
hook which returns the IRQ number of the performance counter.
The hook should return < 0 if the performance counter interrupt is
shared with the timer.  If the hook is not present, the CPU vector
reported in C0_IntCtl (cp0_perfcount_irq) is used.

Signed-off-by: Andrew Bresticker <abrestic@chromium.org>
Reviewed-by: Qais Yousef <qais.yousef@imgtec.com>
Tested-by: Qais Yousef <qais.yousef@imgtec.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Jason Cooper <jason@lakedaemon.net>
Cc: Andrew Bresticker <abrestic@chromium.org>
Cc: Jeffrey Deans <jeffrey.deans@imgtec.com>
Cc: Markos Chandras <markos.chandras@imgtec.com>
Cc: Paul Burton <paul.burton@imgtec.com>
Cc: Qais Yousef <qais.yousef@imgtec.com>
Cc: Jonas Gorski <jogo@openwrt.org>
Cc: John Crispin <blogic@openwrt.org>
Cc: David Daney <ddaney.cavm@gmail.com>
Cc: linux-mips@linux-mips.org
Cc: linux-kernel@vger.kernel.org
Patchwork: https://patchwork.linux-mips.org/patch/7805/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

arch/mips/ath79/irq.c

@@ -359,7 +359,6 @@ void __init arch_init_irq(void)
 		BUG();
 	}
 
-	cp0_perfcount_irq = ATH79_MISC_IRQ(5);
 	mips_cpu_irq_init();
 	ath79_misc_irq_init();