gpio: dwapb: Unify ACPI enumeration checks in get_irq() and configure_irqs()

Shared IRQ is only enabled for ACPI enumeration, there is no need
to have a special flag for that, since we simple can test if device
has been enumerated by ACPI. This unifies the checks in dwapb_get_irq()
and dwapb_configure_irqs().

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Acked-by: Lee Jones <lee.jones@linaro.org>
Acked-by: Serge Semin <fancer.lancer@gmail.com>
Tested-by: Serge Semin <fancer.lancer@gmail.com>