tests/kernel/common: Add nested irq_offload() test

Add a very simple test of the CONFIG_IRQ_OFFSET_NESTED feature that
exercises nested interrupts in a portable way.  It calls irq_offset()
from within a k_timer callback and validates that the return lands
back in the original interrupt successfully.

Signed-off-by: Andy Ross <andrew.j.ross@intel.com>
2 files changed