Consolidate IRQ routines for better maintenance.

While here, rename lp_irq_type() to lp_irq_set_type() to be in align
with a callback name.
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Acked-by: Mika Westerberg <mika.westerberg@linux.intel.com>