torture: Default --no-clocksourcewd on arm64

torture: Default --no-clocksourcewd on arm64

Because arm64 does not support CONFIG_CLOCKSOURCE_WATCHDOG=n kernels,
--do-clocksourcewd gets Kconfig errors.  This commit therefore makes
--do-no-clocksourcewd be the default on arm64.

Note that arm64 users can still specify --do-clocksourcewd in order to
override this default.

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Neeraj Upadhyay (AMD) <neeraj.upadhyay@kernel.org>