boards: use zephyr,sdhc-spi-slot over zephyr,mmc-spi-slot

switch all in tree usage of zephyr,mmc-spi-slot to zephyr,sdhc-spi-slot.
This will change all boards to use the new SD subsystem instead of the
SDMMC SPI driver

Signed-off-by: Daniel DeGrasse <daniel.degrasse@nxp.com>