mmc: sdhci-st: Add support for de-asserting reset signal and top regs resource

STiH407 family SoC's can have a reset signal for the controller which needs to
be managed. Also the eMMC controller has some additional 'top' memory mapped
registers which are used to manage the dynamic and static delay required for
UHS modes. This patch adds support for creating the mapping, which will be used
by subsequent patches.

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>