mfd: Drop the twl4030-irq kthread

... and use threaded IRQ infrastructure. Later
patches will come dropping both workqueues and
setting the nested thread flag.

Signed-off-by: Felipe Balbi <balbi@ti.com>
Reviewed-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>