dt-bindings: soc: ti: pruss: Update bindings for K3 AM65x SoCs

The K3 AM65x SoCs have the next generation of the PRU-ICSS IP, commonly
called ICSSG. The ICSSG IP on K3 SoCs has couple of additional sub-modules
(two IEP and MII_RT sub-modules each vs one, a new MII_G_RT sub-module)
w.r.t previous generation PRU-ICSS IPs. Update the PRUSS bindings for
these newer ICSSG instances including the info for MII_G_RT.

NOTE:
- The usage of the second IEP and MII_RT sub-module instances are yet
  to be determined, and so are yet to be added.

Signed-off-by: Suman Anna <s-anna@ti.com>

Documentation/devicetree/bindings/soc/ti/ti,pruss.txt

@@ -49,6 +49,7 @@ Required Properties:
                        "ti,am4376-pruss-soc-bus" for AM437x family of SoCs
                        "ti,am5728-pruss-soc-bus" for AM57xx family of SoCs
                        "ti,k2g-pruss-soc-bus" for 66AK2G family of SoCs
+                       "ti,am654-icssg-soc-bus" for K3 AM65x family of SoCs
 - reg            : address and size of the PRUSS CFG sub-module register
                    dictating the interconnect configuration
 - #address-cells : should be 1
@@ -61,7 +62,8 @@ SoC-specific Required properties:
 The following are mandatory properties for all OMAP-architecture based SoCs:
 - ti,hwmods      : name of the hwmod associated with the PRUSS instance
 
-The following properties are _required_ only for Keystone 2 66AK2G SoCs only:
+The following properties are _required_ only for Keystone 2 66AK2G SoCs and
+K3 AM65x SoCs only:
 - power-domains  : Should contain a phandle to a PM domain provider node and an
                    args specifier containing the PRUSS SCI device id value. This
                    property is as per the binding,
@@ -82,6 +84,7 @@ Required Properties:
                        "ti,am4376-pruss" for AM437x family of SoCs
                        "ti,am5728-pruss" for AM57xx family of SoCs
                        "ti,k2g-pruss" for 66AK2G family of SoCs
+                       "ti,am654-icssg" for K3 AM65x family of SoCs
 - reg            : base address and size of the entire PRU-ICSS space
 - interrupts     : all the interrupts generated towards the main host
                    processor in the SoC. The format depends on the
@@ -128,6 +131,10 @@ node each for now with specific node names as below:
                   "iep" for IEP sub-module,
                   "mii-rt" for MII-RT sub-module,
 
+The following sub-modules are new and present only on ICSSG IP instances and
+are applicable only for K3 SoCs. They are represented as follows:
+	MII_G_RT sub-module: represent as a syscon node with name "mii-g-rt"
+
 See Documentation/devicetree/bindings/mfd/syscon.txt for generic syscon
 binding details.