dt-bindings: net: snps,dwmac: Add 'ahb' reset/reset-name

According to:
stmmac_platform.c: stmmac_probe_config_dt
stmmac_main.c: stmmac_dvr_probe

dwmac controller may require one (stmmaceth) or two (stmmaceth+ahb)
reset signals, and the maxItems of resets/reset-names is going to be 2.

The gmac of Starfive Jh7110 SOC must have two resets.
it uses snps,dwmac-5.20 IP.
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Samin Guo <samin.guo@starfivetech.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

Documentation/devicetree/bindings/net/snps,dwmac.yaml

@@ -136,12 +136,16 @@ properties:
         - ptp_ref
 
   resets:
-    maxItems: 1
-    description:
-      MAC Reset signal.
+    minItems: 1
+    items:
+      - description: GMAC stmmaceth reset
+      - description: AHB reset
 
   reset-names:
-    const: stmmaceth
+    minItems: 1
+    items:
+      - const: stmmaceth
+      - const: ahb
 
   power-domains:
     maxItems: 1