Testing performed: That a card is successfully mounted on Pygamer with
the built in SD card slot
This module is enabled for most FULL_BUILD boards, but is disabled for
samd21 ("M0"), litex, and pca10100 for various reasons.
Manually specify available modules and disable any modules
that are currently unsupported on the litex target.
Signed-off-by: Sean Cross <sean@xobs.io>