MIPS: Lantiq: Make irq.c support the FALC-ON

MIPS: Lantiq: Make irq.c support the FALC-ON

There are minor differences in how irqs work on xway and falcon socs.  Xway
needs 2 quirks that we need to disable for falcon to also work with this
code.

* EBU irq does not need to send a special ack to the EBU
* The EIU does not exist

Signed-off-by: Thomas Langer <thomas.langer@lantiq.com>
Signed-off-by: John Crispin <blogic@openwrt.org>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/3253/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>