dt-bindings:iio:adc:qcom,pm8018-adc: yaml conversion and rename.

Renamed to match a listed compatible rather than relying on wildcards
with all their usual problems.

Dropped the reference supply as a requirement as at least one dtsi doesn't
include it and the example never did.

Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Cc: Linus Walleij <linus.walleij@linaro.org>
Link: https://lore.kernel.org/r/20201031184854.745828-36-jic23@kernel.org