Enumerate logical hyperthread CPUs manually if they aren't already listed

Enumerate logical hyperthread CPUs manually if they aren't already listed
in the mptable.  The way this works is that we determine if the system
has hyperthreading and how many logical CPU's should be in each physical
CPU by using the information returned by cpuid.  During the first pass of
the mptable, we build a bitmask of the APIC IDs of the CPUs listed in the
mptable.  We then scan that bitmask to see if the CPUs are already listed
by the mptable, or if there are any APIC IDs already in use that would
conflict with the APIC IDs of the logical CPUs.  If that test succeeds,
then we fixup the count of application processors.  Later on during the
second pass of the mptable we create fake processor entries for logical
CPUs and add them to the system.

We only need this type of fixup hack when using the mptable to enumerate
CPUs.  The ACPI MADT table properly enumerates all logical CPUs.