MIPS: Netlogic: SMP fixes for XLR/XLS platform code.

Fix few issues in the Netlogic code:
- Use handle_percpu_irq to handle per-cpu interrupts
- Remove unused function nlm_common_ipi_handler()
- Call scheduler_ipi() on SMP_RESCHEDULE_YOURSELF
- Enable interrupts in nlm_smp_finish()

Signed-off-by: Jayachandran C <jayachandranc@netlogicmicro.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/2460/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>