rcu: Inline preemptible RCU __rcu_read_lock()

Move __rcu_read_lock() from kernel/rcupdate.c to include/linux/rcupdate.h,
allowing the compiler to inline it.

Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Tested-by: Linus Torvalds <torvalds@linux-foundation.org>
2 files changed