ACPI: fix "acpi=ht" boot option

We broke "acpi=ht" in 2.6.32 by disabling MADT parsing
for acpi=disabled.  e5b8fc6ac158f65598f58dba2c0d52ba3b412f52
This also broke systems which invoked acpi=ht via DMI blacklist.

acpi=ht is a really ugly hack,
but restore it for those that still use it.

http://bugzilla.kernel.org/show_bug.cgi?id=14886

Signed-off-by: Len Brown <len.brown@intel.com>