There is some odd indentation here.

You should use ofw_bus_search_compatible, and set the a10 flag in the attach function.

I would suggest putting this last, after all the softc data is set.

This is the original indentation but I can fix that if you want.

This should be changed to __AW_WDOG_H__

Bits 1:0 of A31_WDOG_CONFIG controls the target for the reset signal. 0x1 is "to whole system" and 0x2 is "only interrupt". Maybe A31_WDOG_CONFIG_RST_EN could have a name to better reflect this?

I normally use #define<tab>FOO for the register and #define<tab> FOO_BAR for the contents of the register.

At least wdog_mode_en should be a 32-bit value as it stores the contents of the register. It could be argued the register offsets should be bus_size_t. Given there are only a limited number of copies of this struct the size shouldn't matter too much.

Missing device_set_desc(dev, "Allwinner A10 Watchdog"); (or similar).

Extra return.

You could put a unique value in the compat_data map, then have something like:

switch (ofw_bus_search_compatible(dev, compat_data)->ocd_data) {
case A10:
   ...
   break;
case A31:
   ...
   break;
 default:
   ...
   return (ENXIO);
}

If you move the mtx_init call below this you can remove this line.