genirq: Add IRQCHIP_SET_TYPE_MASKED flag

irq_chips, which require to mask the chip before changing the trigger
type should set this flag. So the core takes care of it and the
requirement for looking into desc->status in the chip goes away.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Linus Walleij <linus.walleij@stericsson.com>
Cc: Lars-Peter Clausen <lars@metafoo.de>