Add support for SPI-mode SDCard interface. Also, add pull-up and
slew constraints to the standard sdcard interface.
Signed-off-by: Gabriel Somlo <gsomlo@gmail.com>
We initially wanted to provide different level of support for the platforms/targets, mainly
to avoid too much maintenance and let each contributor update its contributed platforms and
targets, but it's easier to update all platforms/targets all-together when LiteX evolves or
changes (and that's what has been done on litex-boards since the creation of the repository).
So let just simplify things and avoid this differentiation.
Gabriel Somlo
Florent Kermarrec