mmc: meson-gx: remove Rx phase tuning

This remove all the code related to phase settings. Using the Rx phase
for tuning has not been reliable. We had several issues over the past
months, on both v2 and v3 mmc chips After discussing the issue matter
with Amlogic, They suggested to set a phase shift of 180 between Core and
Tx and use signal resampling for the tuning.

Since we won't be playing with the phase anymore, let's remove all the
clock code related to it and set the appropriate value on init.
Signed-off-by: Jerome Brunet <jbrunet@baylibre.com>
Tested-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Reviewed-by: Kevin Hilman <khilman@baylibre.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>