The rate of the stream does not matter for the fifos of the axg family.
Fifos will just push or pull data to/from the DDR according to consumption
or production of the downstream element, which is the DPCM backend.

Drop the rate list and allow continuous rates. The lower and upper rate are
set according what is known to work with the different backends

This allows the PDM input backend to also use continuous rates.
Signed-off-by: Jerome Brunet <jbrunet@baylibre.com>
Link: https://msgid.link/r/20240223175116.2005407-6-jbrunet@baylibre.comSigned-off-by: Mark Brown <broonie@kernel.org>