mmc: tmio: refactor tuning execution into SDHI driver

mmc: tmio: refactor tuning execution into SDHI driver

Move Renesas specific code for executing the tuning with a SCC into the
SDHI driver and leave only a generic call in the TMIO driver. Simplify
the code a little by removing init_tuning() and prepare_tuning()
callbacks. The latter is directly folded into the new execute_tuning()
callbacks.

Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Reviewed-by: Niklas Söderlund <niklas.soderlund+renesas@ragnatech.se>
Reviewed-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Link: https://lore.kernel.org/r/20200129203709.30493-2-wsa+renesas@sang-engineering.com
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>