disk: stm32: Select `USE_STM32_HAL_SD_EX` on stm32l4
disk: stm32: Select `USE_STM32_HAL_SD_EX` on stm32l4

This commit prepares supporting sdmmc on
stm32l4+ devices. When trying to compile the
sdmmc driver there is a compilation error
because `HAL_SDEx_DriveTransceiver_1_8V_Callback`
is not implemented. We solve this by compiling
also `sd_ex` in cube as this function is implemented
there as weak.

Signed-off-by: Shlomi Vaknin <54c0a9b681c5459019f43c3dc65e0278ef9673d9@gmail.com>

Vudentz/zephyr,galak/zephyr,galak/zephyr,zephyrproject-rtos/zephyr,Vudentz/zephyr,nashif/zephyr,finikorg/zephyr,zephyrproject-rtos/zephyr,Vudentz/zephyr,galak/zephyr,nashif/zephyr,finikorg/zephyr,Vudentz/zephyr,finikorg/zephyr,finikorg/zephyr,zephyrproject-rtos/zephyr,galak/zephyr,galak/zephyr,nashif/zephyr,Vudentz/zephyr,zephyrproject-rtos/zephyr,finikorg/zephyr,nashif/zephyr,nashif/zephyr,zephyrproject-rtos/zephyr,Vudentz/zephyr