ACPI: remove P2B-S from blacklist.

According to http://bugzilla.kernel.org/show_bug.cgi?id=6933


The latest BIOS for the P2B-S works fine.
Remove it from the blacklist.

Signed-off-by: Dave Jones <davej@redhat.com>
Signed-off-by: Len Brown <len.brown@intel.com>