drivers: lora: sx1276: handle NULL callback in irqHandlers
drivers: lora: sx1276: handle NULL callback in irqHandlers

Part of sx1276 driver which is in loramac-node module passes to Zephyr
irqHandlers with callbacks. Some of those callbacks can be NULL and this
is true now (with the current version of loramac-node) for DIO5. If we
define all 0-5 DIOs in dts, then this results in interrupts which are
unwanted. As we do not check that loramac-node callback is NULL, then we
crash trying to call it.

Check every handler during initialization and just skip initialization
of GPIO if it is NULL. This also prevents crashes, because there is no
way GPIO interrupt to be triggered in runtime for this DIO.

Signed-off-by: Marcin Niestroj <63506c06cfbc47ace147db1702f6e751f5ac2132@grinn-global.com>

finikorg/zephyr,galak/zephyr,Vudentz/zephyr,Vudentz/zephyr,zephyrproject-rtos/zephyr,Vudentz/zephyr,galak/zephyr,zephyrproject-rtos/zephyr,nashif/zephyr,Vudentz/zephyr,finikorg/zephyr,galak/zephyr,nashif/zephyr,finikorg/zephyr,Vudentz/zephyr,zephyrproject-rtos/zephyr,galak/zephyr,nashif/zephyr,nashif/zephyr,zephyrproject-rtos/zephyr,nashif/zephyr,finikorg/zephyr,Vudentz/zephyr,galak/zephyr,zephyrproject-rtos/zephyr,finikorg/zephyr