dt-bindings: clock: arm,syscon-icst: Use 'reg' instead of 'vco-offset' for VCO register address

'reg' is the standard property for defining register banks/addresses. Add
it to use for the VCO register address and deprecate 'vco-offset'. This
will also allow for using standard node names with unit-addresses.

Cc: Linus Walleij <[e-mail]>
Cc: Stephen Boyd <[e-mail]>
Cc: [e-mail]
Cc: [e-mail]
Cc: Michael Turquette <[e-mail]>
Signed-off-by: Rob Herring <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Stephen Boyd <[e-mail]>

Documentation/devicetree/bindings/clock/arm,syscon-icst.yaml

···
       - arm,impd1-vco1
       - arm,impd1-vco2
 
+  reg:
+    maxItems: 1
+    description: The VCO register
+
   clocks:
     description: Parent clock for the ICST VCO
     maxItems: 1
···
   vco-offset:
     $ref: '/schemas/types.yaml#/definitions/uint32'
     description: Offset to the VCO register for the oscillator
+    deprecated: true
 
 required:
   - "#clock-cells"