ARM: tegra: colibri_t20: annotate/move sd card detect

Annotate the SD card, its detect pin and move the SD card detect GPIO
definition from the module to the carrier board more in-line with our
other device trees.

Signed-off-by: Marcel Ziswiler <marcel.ziswiler@toradex.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>