rcu: limit PREEMPT_RCU configurations

PREEMPT_LAZY can be enabled stand-alone or alongside PREEMPT_DYNAMIC
which allows for dynamic switching of preemption models.

The choice of PREEMPT_RCU or not, however, is fixed at compile time.

Given that PREEMPT_RCU makes some trade-offs to optimize for latency
as opposed to throughput, configurations with limited preemption
might prefer the stronger forward-progress guarantees of PREEMPT_RCU=n.

Accordingly, explicitly limit PREEMPT_RCU=y to the latency oriented
preemption models: PREEMPT, PREEMPT_RT, and the runtime configurable
model PREEMPT_DYNAMIC.

This means the throughput oriented models, PREEMPT_NONE,
PREEMPT_VOLUNTARY, and PREEMPT_LAZY will run with PREEMPT_RCU=n.

Cc: Paul E. McKenney <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Reviewed-by: Frederic Weisbecker <[email protected]>
Signed-off-by: Ankur Arora <[email protected]>
Signed-off-by: Paul E. McKenney <[email protected]>
Signed-off-by: Boqun Feng <[email protected]>

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