percpu-rwsem: kill CONFIG_PERCPU_RWSEM

Remove CONFIG_PERCPU_RWSEM, the next patch adds the unconditional
user of percpu_rw_semaphore.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>

diff --cc arch/Kconfig
Simple merge

diff --cc init/Kconfig
Simple merge

diff --cc kernel/locking/Makefile
Simple merge

diff --cc lib/Kconfig
Simple merge