rcu: Drive configuration directly from SMP and PREEMPT

This commit eliminates the possibility of running TREE_PREEMPT_RCU
when SMP=n and of running TINY_RCU when PREEMPT=y.  People who really
want these combinations can hand-edit init/Kconfig, but eliminating
them as choices for production systems reduces the amount of testing
required.  It will also allow cutting out a few #ifdefs.

Note that running TREE_RCU and TINY_RCU on single-CPU systems using
SMP-built kernels is still supported.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

commit 8008e129dc90ff4f7a56cb033d6bd042afe3ed52 upstream
Cherry-picked for v3.0-rt and fixed-up merge conflicts
Note: This makes the depends lines for these options in init/Kconfig for v3.0-rt
match those for v3.2-rc2-rt3
Signed-off-by: John Kacur <jkacur@redhat.com>