mmc: stm32_sdmmc2: change the displayed config name

Change the mmc displayed name in U-Boot for stm32_sdmmc2 driver to
“STM32 SD/MMC”.

This stm32_sdmmc2 driver is for version 2 of the ST HW IP SDMMC but the
displayed name "STM32 SDMMC2" is confusing for user, between the
instance of SDMMC and the device identifier of MMC.

For example on EV1 board, we have:

STM32MP1> mmc list
 STM32 SDMMC2: 0 (SD)
 STM32 SDMMC2: 1 (eMMC)

Changed to more clear:

STM32MP1> mmc list
 STM32 SD/MMC: 0 (SD)
 STM32 SD/MMC: 1 (eMMC)

Signed-off-by: Patrick Delaunay <patrick.delaunay@st.com>
Reviewed-by: Patrice Chotard <patrice.chotard@st.com>