imx: kontron-sl-mx8mm: Enable PCA9450 regulator driver and fix SD card access

Currently accessing the SD card on USDHC2 fails with:

=> mmc dev 1
Card did not respond to voltage select! : -110

This is due to the fact that UHS modes are enabled in the defconfig
and the devicetree, but the referenced LDO5 regulator (reg_nvcc_sd)
is not available to switch the data lines from 3.3V to 1.8V mode.

By enabling the regulator driver the vqmmc-supply is now available
and the SD card works also in high speed modes:

=> mmc dev 1
switch to partitions #0, OK
mmc1 is current device

Please note that the board has a GPIO connected to the SD_VSEL signal
of the PMIC. As the driver uses the LDO5CTRL_H register to set the
voltage, we need to make sure that this GPIO (GPIO01_IO4) is set to
a high level.

Signed-off-by: Frieder Schrempf <frieder.schrempf@kontron.de>
Reviewed-by: Fabio Estevam <festevam@denx.de>
Tested-by: Fabio Estevam <festevam@denx.de>