Adds basic infrastructure to allow subsystems to reserve performance
counters on the x86 chips.  Only UP kernels are supported in this patch to
make reviewing easier.  The SMP portion makes a lot more changes.

Think of this as a locking mechanism where each bit represents a different
counter.  In addition, each subsystem should also reserve an appropriate
event selection register that will correspond to the performance counter it
will be using (this is mainly neccessary for the Pentium 4 chips as they
break the 1:1 relationship to performance counters).

This will help prevent subsystems like oprofile from interfering with the
nmi watchdog.
Signed-off-by: Don Zickus <dzickus@redhat.com>
Signed-off-by: Andi Kleen <ak@suse.de>