dt-bindings: net: dsa: mediatek,mt7530: add econet,en7528-switch

The EcoNet EN7528 MIPS SoC integrates an MT7530 Gigabit switch,
memory-mapped in the SoC register space like the built-in switches of
the MediaTek MT7988 and Airoha EN7581/AN7583 SoCs. Its four user ports
are connected to integrated Gigabit PHYs and its CPU port is connected
internally to the SoC Ethernet MAC.

Those three switches are MT7531-based, whereas the EN7528 has a genuine
MT7530 switch core (its chip revision register reads 0x7530). The two
generations differ in their register programming - for example the CPU
port is selected through the MT7530-style MFC register rather than the
MT7531 CFC register - so the EN7528 is not compatible with the existing
switch compatibles and cannot fall back to one of them.

Add the econet,en7528-switch compatible, with the same constraints as
the other built-in switches.

Signed-off-by: Ahmed Naseef <naseefkm@gmail.com>
Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@oss.qualcomm.com>
Link: https://patch.msgid.link/2133035bb22eacc8a0e21f86c0c800a45023ee01.1783770059.git.naseefkm@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Documentation/devicetree/bindings/net/dsa/mediatek,mt7530.yaml

@@ -100,6 +100,10 @@ properties:
           Built-in switch of the Airoha AN7583 SoC
         const: airoha,an7583-switch
 
+      - description:
+          Built-in switch of the EcoNet EN7528 SoC
+        const: econet,en7528-switch
+
   reg:
     maxItems: 1
 
@@ -318,6 +322,7 @@ allOf:
             - mediatek,mt7988-switch
             - airoha,en7581-switch
             - airoha,an7583-switch
+            - econet,en7528-switch
     then:
       $ref: "#/$defs/builtin-dsa-port"
       properties: