Documentation: ARM: sunxi: Add Allwinner SoC T3.

Add Allwinner SoC T3 document and fix format.
Signed-off-by: Hao Zhang <hao5781286@gmail.com>
Signed-off-by: Maxime Ripard <maxime.ripard@bootlin.com>

Documentation/devicetree/bindings/arm/sunxi.txt

@@ -14,7 +14,8 @@ using one of the following compatible strings:
   allwinner,sun8i-a83t
   allwinner,sun8i-h2-plus
   allwinner,sun8i-h3
-  allwinner-sun8i-r40
+  allwinner,sun8i-r40
+  allwinner,sun8i-t3
   allwinner,sun8i-v3s
   allwinner,sun9i-a80
   allwinner,sun50i-a64