MFi386: sync rtc code - don't setup an interrupt handler for irq0 when the lapic timer is active.  Don't enable periodic interrupts unless we are using them.  Replace spl protection with a spinlock.
MFi386: sync rtc code - don't setup an interrupt handler for irq0 when
the lapic timer is active.  Don't enable periodic interrupts unless we are
using them.  Replace spl protection with a spinlock.

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