new sharable twl4030 SIH irq_chip

Add TWL4030 infrastructure for shared SIH interrupts.

This is basically what the twl4030 GPIO IRQ code does, but
switching to a workqueue to handle each irqchip's mask/unmask
and set_type operations instead of a kthread that must figure
out what to do each time it wakes up.

Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Tony Lindgren <tony@atomide.com>