mmc: sti_sdhci: Rework sti_mmc_core_config()

Use struct udevice* as input parameter. Previous
parameters are retrieved through plat and priv data.

This to prepare to use the reset framework.

Signed-off-by: Patrice Chotard <patrice.chotard@st.com>
Reviewed-by: Jaehoon Chung <jh80.chung@samsung.com>
Reviewed-by: Simon Glass <sjg@chromium.org>