RCU: various patches

Andrew,

Please include this patchset for some testing in -mm.

This patchset consists of various merge candidates that would
do well to have some testing in -mm. This patchset breaks
out RCU implementation from its APIs to allow multiple
implementations, gives RCU its own softirq and finally
lines up preemptible RCU from -rt tree as a configurable
RCU implementation for mainline. Published earlier and
re-diffed against -mm. One major change since the last time
is that this has a new implementation of preemptible RCU
from Paul which fixes the problem with watchdog NMI.
For details - http://lkml.org/lkml/2006/10/13/259

They have been tested lightly using combinations of
dbench, kernbench and ltp (both CONFIG_CLASSIC_RCU=y and
CONFIG_RCU_PREEMPT=y) on x86_64 and ppc64. Also ran
rcutorture successfully on my x86_64 box with both
RCU implementations.

Thanks
Dipankar