genirq: record IRQ_LEVEL in irq_desc[]

Impact: fix __irq_set_trigger() for IRQ_LEVEL

When recording the irq trigger type, let's also make sure
that IRQ_LEVEL gets set correctly.

Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Acked-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>