ARC: irq: idu: mask IRQ before level setup

Currently we setup irq trigger type (pulse or level) in IDU
before we Mask (disable) IRQ line.

The IDU is disabled at this moment, however we still may
accidentally generate interrupt by trigger setup.

To avoid that let's mask (disable) IRQ before trigger type setup.

Signed-off-by: Eugeniy Paltsev <Eugeniy.Paltsev@synopsys.com>
Signed-off-by: Evgeniy Paltsev <PaltsevEvgeniy@gmail.com>