mfd: twl4030-core irq simplification

Simplify twl4030 IRQ handling by removing a needless custom flow
handler.  The top level IRQs, from the PIH, are well suited for
handle_simple_irq() ... they can't be acked or masked.

Switching resolves some issues with how IRQs were dispatched.
Notably, abuse of desc->status, IRQ accounting, and handling
of various faults.

In short, use standard genirq code.

Drivers that request_irq() to the PIH will need to pay more
attention to things like setting IRQF_DISABLED (since it's
no longer ignored), and making I2C calls from handlers (you'll
need a lockdep workaround).

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