ACPI: acpi_pad: Don't needlessly mark LAPIC unstable

As suggested in Venki's suggestion in the commit 0dc698b9,
add LAPIC unstable detection in the acpi_pad drvier too.

Signed-off-by: Chen Gong <gong.chen@linux.intel.com>
Signed-off-by: Len Brown <len.brown@intel.com>