genirq: Add state field to irq_data

Some chip implementations need to access certain status flags. With
sparse irqs that requires a lookup of the irq descriptor. Add a state
field which contains such flags.

Name it in a way which will make coders happy to access it with the
proper accessor functions. And it's easy to grep for.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>