drivers/apbuart: fix polling mode
drivers/apbuart: fix polling mode

Header file generation from device tree was failing in pulling mode.
Restrict the interrupt node usage to interrupt mode only.

Signed-off-by: Romain Mahoux <b8aabb4b95c817d9df69b6be95b2b94d6b1efe17@mahoux.fr>

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