watchdog: bindings: Remove obsolete platforms from dt doc.

STiH415/6 SoC support is being removed from the kernel
so update the dt bding document to reflect this.

Signed-off-by: Peter Griffin <peter.griffin@linaro.org>
Cc: <linux-watchdog@vger.kernel.org>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@iguana.be>

Documentation/devicetree/bindings/watchdog/st_lpc_wdt.txt

@@ -9,8 +9,7 @@ functionality.
 
 Required properties
 
-- compatible 	: Must be one of: "st,stih407-lpc" "st,stih416-lpc"
-				  "st,stih415-lpc" "st,stid127-lpc"
+- compatible 	: Should be: "st,stih407-lpc"
 - reg		: LPC registers base address + size
 - interrupts    : LPC interrupt line number and associated flags
 - clocks	: Clock used by LPC device (See: ../clock/clock-bindings.txt)