mmc: mmci: stm32: define get_dctrl_cfg

This patch defines get_dctrl_cfg callback for sdmmc variant.
sdmmc variant has specific stm32 transfer modes.
sdmmc data transfer mode selection could be:
-Block data transfer ending on block count.
-SDIO multibyte data transfer.
-MMC Stream data transfer (not used).
-Block data transfer ending with STOP_TRANSMISSION command.

Signed-off-by: Ludovic Barre <ludovic.barre@st.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>