dt-bindings: watchdog: Convert DW WDT binding to DT schema

Modern device tree bindings are supposed to be created as YAML-files
in accordance with dt-schema. This commit replaces the DW Watchdog
legacy bare text bindings with YAML file. As before the binding states
that the corresponding dts node is supposed to have a registers
range, a watchdog timer references clock source, optional reset line and
pre-timeout interrupt.

Signed-off-by: Serge Semin <Sergey.Semin@baikalelectronics.ru>
Reviewed-by: Rob Herring <robh@kernel.org>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Cc: Alexey Malahov <Alexey.Malahov@baikalelectronics.ru>
Cc: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: linux-mips@vger.kernel.org
Link: https://lore.kernel.org/r/20200530073557.22661-2-Sergey.Semin@baikalelectronics.ru


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