pico-imx7d: add baseboard SD card boot detect

Technexion PICO-IMX7 SoM is supporting USDHC3 (eMMC or micro SD on SoM)
and USDHC1 (SD on carrier board) to use on any carrier board like
PICO-NYMPH. Based on the U-Boot version from Technexion it adds
baseboard SD card boot detect to able to boot from selected USDHC1
or USDHC3 boot devices.

Signed-off-by: Benjamin Szőke <egyszeregy@freemail.hu>
Tested-by: Fabio Estevam <festevam@gmail.com>
5 files changed