irqchip/i8259: Fix shutdown order by moving syscore_ops registration

When using cpufreq on Loongson 2F MIPS platform, "poweroff"
command gets frequently stuck in syscore_shutdown(). The reason is
that i8259A_shutdown() gets called before cpufreq_suspend(), and if we
have pending work then irq_work_sync() in cpufreq_dbs_governor_stop()
gets stuck forever as we have all interrupts masked already.

irq-i8259 is registering syscore_ops using device_initcall(),
while cpufreq uses core_initcall(). Fix the shutdown order simply
by registering the irq syscore_ops during the early IRQ init instead
of using a separate initcall at later stage.

Signed-off-by: Aaro Koskinen <aaro.koskinen@iki.fi>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>