tests/kernel/context: add case for CONFIG_APIC_TIMER

Test needs trivial modification to account for new APIC timer code.
Eventually CONFIG_APIC_TIMER_IRQ, CONFIG_LOAPIC_TIMER_IRQ, etc. will
be consolidated into one CONFIG_TIMER_IRQ to reduce the noise a bit.

Signed-off-by: Charles E. Youse <charles.youse@intel.com>