MIPS: lantiq: Fix IPI interrupt handling

MIPS: lantiq: Fix IPI interrupt handling

This makes SMP on the vrx200 work again, by removing all the MIPS CPU
interrupt specific code and making it fully use the generic MIPS CPU
interrupt controller.

The mti,cpu-interrupt-controller from irq-mips-cpu.c now handles the CPU
interrupts and also the IPI interrupts which are used to communication
between the CPUs in a SMP system. The generic interrupt code was
already used before but the interrupt vectors were overwritten again
when we called set_vi_handler() in the lantiq interrupt driver and we
also provided our own plat_irq_dispatch() function which overwrote the
weak generic implementation. Now the code uses the generic handler for
the MIPS CPU interrupts including the IPI interrupts and registers a
handler for the CPU interrupts which are handled by the lantiq ICU with
irq_set_chained_handler() which was already called before.

Calling the set_c0_status() function is also not needed any more because
the generic MIPS CPU interrupt already activates the needed bits.

Fixes: 1eed40043579 ("MIPS: smp-mt: Use CPU interrupt controller IPI IRQ domain support")
Cc: stable@kernel.org # v4.12
Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>
Signed-off-by: Paul Burton <paul.burton@mips.com>
Cc: jhogan@kernel.org
Cc: ralf@linux-mips.org
Cc: john@phrozen.org
Cc: linux-mips@linux-mips.org
Cc: linux-mips@vger.kernel.org