ARM: orion: provide C-style interrupt handler for MULTI_IRQ_HANDLER

DT-enabled Marvell Kirkwood and Dove SoCs make use of an irqchip
driver. As expected for irqchip drivers, it uses a C-style
interrupt handler and therefore selects MULTI_IRQ_HANDLER.

Now, compiling a kernel with both non-DT and DT support enabled,
selecting MULTI_IRQ_HANDLER will break ASM irq handler used by
non-DT boards.

Therefore, we provide a C-style irq handler even for non-DT boards,
if MULTI_IRQ_HANDLER is set. By installing the C-style irq handler
in orion_irq_init this is transparent to all non-DT board files.

While the regression report was filed on Marvell Kirkwood, also
Marvell Dove non-DT boards are affected and fixed by this patch.

Signed-off-by: Sebastian Hesselbarth <sebastian.hesselbarth@gmail.com>
Tested-by: Ian Campbell <ijc@hellion.org.uk>
Reported-by: Ian Campbell <ijc@hellion.org.uk>
Cc: <stable@vger.kernel.org> # v3.12+
Fixes: 2326f043 ("ARM: kirkwood: convert to DT irqchip and clocksource")
Fixes: f07d73e3 ("ARM: dove: convert to DT irqchip and clocksource")
Acked-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: Jason Cooper <jason@lakedaemon.net>