Avoids per_cpu calculations and also prepares for call_rcu_bh().

At OLS, Rusty had suggested getting rid of many per_cpu() calculations in RCU
code and making the code simpler.  I had already done that for the rcu-softirq
patch earlier, so I am splitting that into two patch.  This first patch cleans
up the macros and uses pointers to the rcu per-cpu data directly to manipulate
the callback queues.  This is useful for the call-rcu-bh patch (to follow)
which introduces a new RCU mechanism - call_rcu_bh().  Both generic and
softirq rcu can then use the same code, they work different global and percpu
data.
Signed-off-by: Dipankar Sarma <dipankar@in.ibm.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>