mmc: core: Only execute tuning for SDR50 and SDR104

Only execute tuning for sd and sdio devices that are using
SDR50 or SDR104.

Make sure clock is hold during tuning for sdio devices.

Signed-off-by: Fredrik Soderstedt <fredrik.soderstedt@stericsson.com>
Acked-by: Johan Rudholm <jrudholm@gmail.com>
Acked-by: Ulf Hansson <ulf.hansson@linaro.org>
Signed-off-by: Chris Ball <cjb@laptop.org>