dt-bindings: power: supply: bq25890: use one fallback compatible

BQ2589[0256] seem compatible between each other in major aspects and
remaining features are auto-detectable (by reading device revision ID
register).  Existing DTS already uses the compatibles with a fallback,
so adjust the bindings to reflect this and fix dtbs_check warning:

  arch/arm64/boot/dts/freescale/imx8mq-librem5-r2.dtb: charger@6a: compatible: ['ti,bq25895', 'ti,bq25890'] is too long
Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>

Documentation/devicetree/bindings/power/supply/bq25890.yaml

@@ -15,11 +15,15 @@ allOf:
 
 properties:
   compatible:
-    enum:
+    oneOf:
+      - enum:
           - ti,bq25890
+      - items:
+          - enum:
               - ti,bq25892
               - ti,bq25895
               - ti,bq25896
+          - const: ti,bq25890
 
   reg:
     maxItems: 1