watchdog: arm_smc_wdt: get wdt status through SMCWD_GET_TIMELEFT

watchdog: arm_smc_wdt: get wdt status through SMCWD_GET_TIMELEFT

The optional SMCWD_GET_TIMELEFT command can be used to detect if
the watchdog has already been started.
See the implementation in OP-TEE secure OS [1].

At probe time, check if the watchdog is already started and then
call wdt_set_force_autostart(). This will keep U-Boot pinging the
watchdog even when the property 'u-boot,noautostart' is present.

Link: https://github.com/OP-TEE/optee_os/commit/a7f2d4bd8632
Signed-off-by: Antonio Borneo <antonio.borneo@foss.st.com>
Reviewed-by: Patrice Chotard <patrice.chotard@foss.st.com>