x86, mrst: Fix APB timer per cpu clockevent

The current APB timer code incorrectly registers a static copy of the
clockevent device for the boot CPU. The per cpu clockevent should be
used instead.

This bug was hidden by zero-initialized data; as such it did not get
exposed in testing, but was discovered by code review.

Signed-off-by: Jacob Pan <jacob.jun.pan@linux.intel.com>
LKML-Reference: <1267592494-7723-1-git-send-email-jacob.jun.pan@linux.intel.com>
Signed-off-by: H. Peter Anvin <hpa@zytor.com>