watchdog: orion: Introduce a SoC-specific RSTOUT mapping

Separate the RSTOUT register mapping for the different compatible strings
supported by the driver. This allows to use devm_ioremap on SoC variants that
share the RSTOUT register, and devm_ioremap_resource (which requests the MMIO
region) on SoCs that have a dedicated RSTOUT register.

Signed-off-by: Ezequiel Garcia <ezequiel.garcia@free-electrons.com>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Acked-by: Jason Cooper <jason@lakedaemon.net>
Tested-by: Jason Gunthorpe <jgunthorpe@obsidianresearch.com>
Tested-by: Sebastian Hesselbarth <sebastian.hesselbarth@gmail.com>
Signed-off-by: Wim Van Sebroeck <wim@iguana.be>