feat(st-sdmmc2): manage cards power cycle

To correctly initialize the MMC devices, a power cycle is required.
For this we need to:
- disable vmmc-supply regulator
- make the power cycle required for SDMMC2 peripheral
- enable regulators

Change-Id: I2be6d9082d1cc4c864a82cf2c31ff8522e2d31a2
Signed-off-by: Yann Gautier <yann.gautier@st.com>