MIPS: oprofile: Only do performance counter handling for counter interrupts

In Loongson2f IP6 is shared by bonito and perfcounters so we need to avoid
do_IRQ for perfcounter when the interrupt is from bonito.

Signed-off-by: Wu Zhangjin <wuzhangjin@gmail.com>
Cc: linux-mips@linux-mips.org
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>