media: Documentation: dt-bindings: media: add AST2600 Video Engine support

The AST2600 has Video Engine so add the compatible string into the
document.
Signed-off-by: Jae Hyun Yoo <jae.hyun.yoo@linux.intel.com>
Acked-by: Joel Stanley <joel@jms.id.au>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>

Documentation/devicetree/bindings/media/aspeed-video.txt

 * Device tree bindings for Aspeed Video Engine
 
-The Video Engine (VE) embedded in the Aspeed AST2400 and AST2500 SOCs can
+The Video Engine (VE) embedded in the Aspeed AST2400/2500/2600 SOCs can
 capture and compress video data from digital or analog sources.
 
 Required properties:
  - compatible:		"aspeed,ast2400-video-engine" or
-			"aspeed,ast2500-video-engine"
+			"aspeed,ast2500-video-engine" or
+			"aspeed,ast2600-video-engine"
  - reg:			contains the offset and length of the VE memory region
  - clocks:		clock specifiers for the syscon clocks associated with
 			the VE (ordering must match the clock-names property)