dt-bindings:iio:pressure:meas,ms5611 yaml conversion.

One addition here was to put in a 20MHz maximum for the SPI bus
as specified in the datasheets of both support parts.

Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Cc: Tomasz Duszynski <tduszyns@gmail.com>
Link: https://lore.kernel.org/r/20201031134110.724233-8-jic23@kernel.org