iio: accel: st_accel: handle deprecated bindings

The earlier deployed LIS3LV02DL driver had already defined a few
DT bindings that need to be supported by the new more generic
driver and listed as compatible but deprecated bindings in the
documentation.

After this we can start to activate the new driver with the old
systems where applicable.

As part of this enablement: make us depend on the old drivers
not being in use so we don't get a kernel with two competing
drivers.

Cc: devicetree@vger.kernel.org
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>