enable the interrupt functionality for sx1509b gpio expander,
when the CONFIG_GPIO_SX1509B_INTERRUPT config is enabled.
The gpio pin used for interrupt should be configured in the
device tree sx1509b node before enabling the interrupt
configuration.
Signed-off-by: Viraaj Somayajula <sviraaj@zedblox.com>
Signed-off-by: Peter Bigot <peter.bigot@nordicsemi.no>
