arch: arc: arcv2_irq_unit.h: MISRA C violation fix.
arch: arc: arcv2_irq_unit.h: MISRA C violation fix.

The function _arc_v2_irq_unit_is_in_isr computes a Boolean
value but the function returns a integer value.
Fix the return type of the function.

This makes the zephyr api _is_in_isr() return a boolean type.
Thereby making it consistent across all the architectures.

Signed-off-by: Adithya Baglody <06b44f6fa9a97a2b955c2d2cd070279967447860@intel.com>

galak/zephyr,punitvara/zephyr,nashif/zephyr,GiulianoFranchetto/zephyr,finikorg/zephyr,galak/zephyr,finikorg/zephyr,ldts/zephyr,nashif/zephyr,Vudentz/zephyr,zephyrproject-rtos/zephyr,ldts/zephyr,explora26/zephyr,finikorg/zephyr,Vudentz/zephyr,GiulianoFranchetto/zephyr,punitvara/zephyr,zephyrproject-rtos/zephyr,explora26/zephyr,finikorg/zephyr,galak/zephyr,zephyrproject-rtos/zephyr,explora26/zephyr,ldts/zephyr,GiulianoFranchetto/zephyr,nashif/zephyr,Vudentz/zephyr,zephyrproject-rtos/zephyr,galak/zephyr,punitvara/zephyr,GiulianoFranchetto/zephyr,zephyrproject-rtos/zephyr,nashif/zephyr,GiulianoFranchetto/zephyr,Vudentz/zephyr,punitvara/zephyr,punitvara/zephyr,galak/zephyr,Vudentz/zephyr,explora26/zephyr,Vudentz/zephyr,ldts/zephyr,ldts/zephyr,nashif/zephyr,explora26/zephyr,finikorg/zephyr