dt-bindings:iio:adc:amlogic,meson-saradc yaml conversion

dt-bindings:iio:adc:amlogic,meson-saradc yaml conversion

This binding is non trivial due to the range of different parts
supported having several subtle quirks. Martin has helped
clarify some of them.

Note, I haven't restricted the amlogic,hhi-sysctrl to only
be present on the relevant parts if nvmem stuff also is, but
it would seem to be rather odd if it were otherwise.

Perhaps we look to make this binding more restrictive at a later date.

Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Reviewed-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Cc: Kevin Hilman <khilman@baylibre.com>
Cc: Neil Armstrong <narmstrong@baylibre.com>
Cc: Jerome Brunet <jbrunet@baylibre.com>
Link: https://lore.kernel.org/r/20200920135436.199003-2-jic23@kernel.org