tests: kernel/common: IRQ offload test if CONFIG_IRQ_OFFLOAD=y

This changes to compile the IRQ offload test only if
CONFIG_IRQ_OFFLOAD=y. For architectures that do not support
IRQ offload (or that developers with to disable IRQ offload
during bring-up), compiling the code would result in linking
errors.

Signed-off-by: Daniel Leung <daniel.leung@intel.com>