genirq: Correctly configure the trigger on chained interrupts

genirq: Correctly configure the trigger on chained interrupts

Commit 1e2a7d78499e ("irqdomain: Don't set type when mapping an IRQ")
moved the trigger configuration call from the irqdomain mapping to
the interrupt being actually requested.

This patch failed to handle the case where we configure a chained
interrupt, which doesn't get requested through the usual path.

In order to solve this, let's call __irq_set_trigger just before
starting the cascade interrupt. Special care must be taken to
make the flow handler stick, as the .irq_set_type method could
have reset it (it doesn't know we're dealing with a chained
interrupt).

Based on an initial patch by Jon Hunter.

Fixes: 1e2a7d78499e ("irqdomain: Don't set type when mapping an IRQ")
Reported-by: John Stultz <john.stultz@linaro.org>
Reported-by: Linus Walleij <linus.walleij@linaro.org>
Tested-by: John Stultz <john.stultz@linaro.org>
Acked-by: Jon Hunter <jonathanh@nvidia.com>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>