This patch adds support for WDIOC_GETTIMELEFT IOCTL in watchdog core. So, there
is another function pointer added to struct watchdog_ops, which can be passed by
drivers to support this IOCTL.

Related documentation is updated too.
Signed-off-by: NViresh Kumar <viresh.kumar@st.com>
Signed-off-by: NLinus Walleij <linus.walleij@linaro.org>
Signed-off-by: NWim Van Sebroeck <wim@iguana.be>