selftests: watchdog: Add gettimeout and get|set pretimeout

Add command line arguments to call ioctl WDIOC_GETTIMEOUT,
WDIOC_GETPRETIMEOUT and WDIOC_SETPRETIMEOUT.

Signed-off-by: Jerry Hoemann <jerry.hoemann@hpe.com>
Signed-off-by: Shuah Khan (Samsung OSG) <shuah@kernel.org>