doc: marvell: add CM3 address space and PPv2.3 description

Patch adds CM3 address space and PPv2.3 description.
Signed-off-by: Stefan Chulski <stefanc@marvell.com>
Acked-by: Marcin Wojtas <mw@semihalf.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Documentation/devicetree/bindings/net/marvell-pp2.txt

 * Marvell Armada 375 Ethernet Controller (PPv2.1)
   Marvell Armada 7K/8K Ethernet Controller (PPv2.2)
+  Marvell CN913X Ethernet Controller (PPv2.3)
 
 Required properties:
 
@@ -12,10 +13,11 @@ Required properties:
 	- common controller registers
 	- LMS registers
 	- one register area per Ethernet port
-  For "marvell,armada-7k-pp2", must contain the following register
+  For "marvell,armada-7k-pp2" used by 7K/8K and CN913X, must contain the following register
   sets:
 	- packet processor registers
 	- networking interfaces registers
+	- CM3 address space used for TX Flow Control
 
 - clocks: pointers to the reference clocks for this device, consequently:
 	- main controller clock (for both armada-375-pp2 and armada-7k-pp2)
@@ -81,7 +83,7 @@ Example for marvell,armada-7k-pp2:
 
 cpm_ethernet: ethernet@0 {
 	compatible = "marvell,armada-7k-pp22";
-	reg = <0x0 0x100000>, <0x129000 0xb000>;
+	reg = <0x0 0x100000>, <0x129000 0xb000>, <0x220000 0x800>;
 	clocks = <&cpm_syscon0 1 3>, <&cpm_syscon0 1 9>,
 		 <&cpm_syscon0 1 5>, <&cpm_syscon0 1 6>, <&cpm_syscon0 1 18>;
 	clock-names = "pp_clk", "gop_clk", "mg_clk", "mg_core_clk", "axi_clk";