arc: interrupt_controller: increase irq unit priority
arc: interrupt_controller: increase irq unit priority

arc_v2_irq_unit_init function will init all interrupts and disable
they, we must make sure we call it first before we use interrupts.
so we need to increase its priority to highest in PRE_KERNEL_1 stage.

Signed-off-by: Watson Zeng <bb6a45ebfbb8932a11537002b062f5218879c562@synopsys.com>

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