TWL603X: IRQ: Migration to IRQ threaded handler

1)Removed request_irq() and replaced it with request_threaded_irq().

2)Removed generic_handle_irq() and replaced it with handle_nested_irq().
  Handling these interrupts is nested, as we are handling an interrupt
  (for e.g rtc,mmc1) when we are still servicing TWL irq.

Change-Id: I2eb46653a676ce8481fb934e02e8cc7e3e87df02
Signed-off-by: Naga Venkata Srikanth V <vnv.srikanth@samsung.com>
Signed-off-by: Oleg_Kosheliev <oleg.kosheliev@ti.com>