mmc: sdhci-st: Add st_mmcss_cconfig function to configure mmcss glue registers.

STiH407 family SoC's have glue registers in the flashSS subsystem which
are used to configure the Arasan HC. This patch configures these glue
registers according to what has been specified in the DT.

Signed-off-by: Peter Griffin <peter.griffin@linaro.org>
Signed-off-by: Giuseppe Cavallaro <peppe.cavallaro@st.com>
Acked-by: Maxime Coquelin <maxime.coquelin@st.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>