tests: nested_irq: Fix k_busy_wait usage and interrupt priority
tests: nested_irq: Fix k_busy_wait usage and interrupt priority

k_busy_wait() call used in test expects time in us, but the test
is specifying wait in ms.

Also the test fails on NRF5 platform as the test hardcodes the
interrupts priority to 0 and 1 and assumes system timer to be of
priority 0 which is not the case in NRF5 platforms as per
@pizi-nordic where system timer is at priority 1. Hence changing
test interrupts to 1 and 2.

Signed-off-by: Spoorthi K <c4ff46ff4cba9c2c6c6c9d55497ae534451b4309@intel.com>

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