mmc: meson-gx: add signal resampling tuning

Use signal resampling tuning for the UHS and HS200 modes.
Instead of trying to get the *best* resampling setting with complex
window calculation, we just stop on the first working setting.

If the tuning setting later proves unstable, we will just continue the
tuning where we left it.

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>