dt-bindings: watchdog: aspeed: External reset signal properties

For the AST2500 and compatible watchdog controllers the external reset
signal can be configured for push-pull or open-drain drive types, and in
the case of push-pull driving, active low or high.

Signed-off-by: Andrew Jeffery <[e-mail]>
Acked-by: Rob Herring <[e-mail]>
Reviewed-by: Guenter Roeck <[e-mail]>
Signed-off-by: Guenter Roeck <[e-mail]>
Signed-off-by: Wim Van Sebroeck <[e-mail]>

Documentation/devicetree/bindings/watchdog/aspeed-wdt.txt

···
         - none: No reset is performed on timeout. Assumes another watchdog
                 engine is responsible for this.
 
+ - aspeed,alt-boot:    If property is present then boot from alternate block.
  - aspeed,external-signal: If property is present then signal is sent to
 			external reset counter (only WDT1 and WDT2). If not
 			specified no external signal is sent.
- - aspeed,alt-boot:    If property is present then boot from alternate block.
+ - aspeed,ext-pulse-duration: External signal pulse duration in microseconds
+
+Optional properties for AST2500-compatible watchdogs:
+ - aspeed,ext-push-pull: If aspeed,external-signal is present, set the pin's
+			 drive type to push-pull. The default is open-drain.
+ - aspeed,ext-active-high: If aspeed,external-signal is present and and the pin
+			   is configured as push-pull, then set the pulse
+			   polarity to active-high. The default is active-low.
 
 Example: