rcutorture: Add SRCU Kconfig-fragment files

Use .boot facility to ease inclusion of SRCU into automated testing.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Greg KH <gregkh@linuxfoundation.org>

diff --cc tools/testing/selftests/rcutorture/configs/SRCU-N
Simple merge

diff --cc tools/testing/selftests/rcutorture/configs/SRCU-N.boot
Simple merge

diff --cc tools/testing/selftests/rcutorture/configs/SRCU-P
Simple merge

diff --cc tools/testing/selftests/rcutorture/configs/SRCU-P.boot
Simple merge