Document: DT: Add bindings for mediatek MT8173 SoC Platform

MT8173 is a 64-bit four core Soc.
And mt8173-evb is a evaluation board based on mt8173.
This commit add the devicetree binding document for
  mediatek MT8173 SoC
  MT8173 sysirq
  MT8173 uart
Signed-off-by: Eddie Huang <eddie.huang@mediatek.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Matthias Brugger <matthias.bgg@gmail.com>

Documentation/devicetree/bindings/arm/mediatek.txt

@@ -9,6 +9,7 @@ compatible: Must contain one of
    "mediatek,mt6592"
    "mediatek,mt8127"
    "mediatek,mt8135"
+   "mediatek,mt8173"
 
 
 Supported boards:
@@ -25,3 +26,6 @@ Supported boards:
 - MTK mt8135 tablet EVB:
     Required root node properties:
       - compatible = "mediatek,mt8135-evbp1", "mediatek,mt8135";
+- MTK mt8173 tablet EVB:
+    Required root node properties:
+      - compatible = "mediatek,mt8173-evb", "mediatek,mt8173";

Documentation/devicetree/bindings/arm/mediatek/mediatek,sysirq.txt

@@ -5,6 +5,7 @@ interrupt.
 
 Required properties:
 - compatible: should be one of:
+	"mediatek,mt8173-sysirq"
 	"mediatek,mt8135-sysirq"
 	"mediatek,mt8127-sysirq"
 	"mediatek,mt6589-sysirq"

Documentation/devicetree/bindings/serial/mtk-uart.txt

@@ -2,9 +2,11 @@
 
 Required properties:
 - compatible should contain:
+  * "mediatek,mt8173-uart" for MT8173 compatible UARTS
   * "mediatek,mt6589-uart" for MT6589 compatible UARTS
   * "mediatek,mt6582-uart" for MT6582 compatible UARTS
-  * "mediatek,mt6577-uart" for all compatible UARTS (MT6589, MT6582, MT6577)
+  * "mediatek,mt6577-uart" for all compatible UARTS (MT8173, MT6589, MT6582, 
+	MT6577)
 
 - reg: The base address of the UART register bank.