The PPC64 interrupt code includes a hook to call when an exception
from the performance monitor unit occurs.  However, there's no way of
reserving the hook properly, so if more than one bit of code tries to
use it things will get ugly.  Currently oprofile is the only user, but
there are likely to be more in future e.g. perfctr, if and when it
reaches a fit state for merging.

This patch creates functions to reserve and release the performance
monitor hardware (including its interrupt), and makes oprofile use
them.  It also creates a new arch/ppc64/kernel/pmc.c, in which we can
put any future helper functions for handling the performance monitor
counters.
Signed-off-by: David Gibson <dwg@au1.ibm.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>