mfd: Make twl-core not depend on pdata->irq_base/end

With sparse IRQs the driver shouldn't depend at all on
any IRQ values coming from board-file.

Remove every occurences of pdata->irq_base/end.

Signed-off-by: Felipe Balbi <balbi@ti.com>
Signed-off-by: Benoit Cousson <b-cousson@ti.com>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>