ARM: orion5x: fix legacy orion5x IRQ numbers

Since v3.18, attempts to deliver IRQ0 are rejected, breaking orion5x.
Fix this by increasing all interrupts by one, as did 5d6bed2a9c8b for
dove. Also, force MULTI_IRQ_HANDLER for all orion platforms (including
dove) as the specific handler is needed to shift back IRQ numbers by
one.

[gregory.clement@free-electrons.com]: moved the select
MULTI_IRQ_HANDLER from PLAT_ORION_LEGACY to ARCH_ORION5X as it broke
the build for dove.

Fixes: a71b092a9c68 ("ARM: Convert handle_IRQ to use __handle_domain_irq")
Signed-off-by: Benjamin Cama <benoar@dolka.fr>
Signed-off-by: Gregory CLEMENT <gregory.clement@free-electrons.com>
Cc: <stable@vger.kernel.org>
Tested-by: Detlef Vollmann <dv@vollmann.ch>

diff --cc arch/arm/Kconfig
Simple merge

diff --cc arch/arm/mach-orion5x/include/mach/irqs.h
Simple merge

diff --cc arch/arm/mach-orion5x/irq.c
Simple merge