dt: fix broken links due to txt->yaml renames

There are some new broken doc links due to yaml renames
at DT. Developers should really run:

	./scripts/documentation-file-ref-check

in order to solve those issues while submitting patches.
This tool can even fix most of the issues with:

	./scripts/documentation-file-ref-check --fix

Acked-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
Acked-by: Mark Brown <broonie@kernel.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Link: https://lore.kernel.org/r/0e4a7f0b7efcc8109c8a41a2e13c8adde4d9c6b9.1592203542.git.mchehab+huawei@kernel.org
Signed-off-by: Rob Herring <robh@kernel.org>

Documentation/devicetree/bindings/display/bridge/sii902x.txt

@@ -37,7 +37,7 @@ Optional properties:
 	simple-card or audio-graph-card binding. See their binding
 	documents on how to describe the way the sii902x device is
 	connected to the rest of the audio system:
-	Documentation/devicetree/bindings/sound/simple-card.txt
+	Documentation/devicetree/bindings/sound/simple-card.yaml
 	Documentation/devicetree/bindings/sound/audio-graph-card.txt
 	Note: In case of the audio-graph-card binding the used port
 	index should be 3.

Documentation/devicetree/bindings/display/rockchip/rockchip-drm.yaml

@@ -24,7 +24,7 @@ properties:
     description: |
       Should contain a list of phandles pointing to display interface port
       of vop devices. vop definitions as defined in
-      Documentation/devicetree/bindings/display/rockchip/rockchip-vop.txt
+      Documentation/devicetree/bindings/display/rockchip/rockchip-vop.yaml
 
 required:
   - compatible

Documentation/devicetree/bindings/net/mediatek-bluetooth.txt

@@ -3,7 +3,7 @@ MediaTek SoC built-in Bluetooth Devices
 
 This device is a serial attached device to BTIF device and thus it must be a
 child node of the serial node with BTIF. The dt-bindings details for BTIF
-device can be known via Documentation/devicetree/bindings/serial/8250.txt.
+device can be known via Documentation/devicetree/bindings/serial/8250.yaml.
 
 Required properties:
 

Documentation/devicetree/bindings/sound/audio-graph-card.txt

@@ -5,7 +5,7 @@ It is based on common bindings for device graphs.
 see ${LINUX}/Documentation/devicetree/bindings/graph.txt
 
 Basically, Audio Graph Card property is same as Simple Card.
-see ${LINUX}/Documentation/devicetree/bindings/sound/simple-card.txt
+see ${LINUX}/Documentation/devicetree/bindings/sound/simple-card.yaml
 
 Below are same as Simple-Card.
 

Documentation/devicetree/bindings/sound/st,sti-asoc-card.txt

@@ -5,7 +5,7 @@ codec or external codecs.
 
 sti sound drivers allows to expose sti SoC audio interface through the
 generic ASoC simple card. For details about sound card declaration please refer to
-Documentation/devicetree/bindings/sound/simple-card.txt.
+Documentation/devicetree/bindings/sound/simple-card.yaml.
 
 1) sti-uniperiph-dai: audio dai device.
 ---------------------------------------