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 <linus.walleij@linaro.org>
Cc: Stephen Boyd <sboyd@kernel.org>
Cc: linux-arm-kernel@lists.infradead.org
Cc: linux-clk@vger.kernel.org
Cc: Michael Turquette <mturquette@baylibre.com>
Signed-off-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20210913192816.1225025-5-robh@kernel.org


Signed-off-by: Stephen Boyd <sboyd@kernel.org>