watchdog: rzg2l_wdt: Add set_timeout callback

This patch adds support for set_timeout callback.

Once WDT is started, the WDT cycle setting register(WDTSET) can be updated
only after issuing a module reset. Otherwise, it will ignore the writes
and will hold the previous value. This patch updates the WDTSET register
if it is active.

Signed-off-by: Biju Das <biju.das.jz@bp.renesas.com>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Link: https://lore.kernel.org/r/20220225175320.11041-8-biju.das.jz@bp.renesas.com


Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@linux-watchdog.org>