watchdog: versal: Add support for expire now

Wdt expire command makes the wdt to count least possible ticks(1)
and expires immediately. Add expire_now option to the xlnx_wwdt_ops
and implement it by calling xlnx_wwdt_start() with minimum possible
count(1).

Signed-off-by: Ashok Reddy Soma <ashok.reddy.soma@xilinx.com>
Link: https://lore.kernel.org/r/1632808919-8600-3-git-send-email-ashok.reddy.soma@xilinx.com


Signed-off-by: Michal Simek <michal.simek@xilinx.com>