Litex add litespi flash and watchdog

[maass-hamburg]

• Be able to use spi flash from LiteSPI.
• Adds watchdog

[maass-hamburg]

Fixed the ci and updated the it to use https://github.com/YosysHQ/oss-cad-suite-build, which contains yosys, prjoxide and nextpnr, so we don't have to compile and install it our self.

[maass-hamburg]

@enjoy-digital @tgorochowik you might want to take a look

[maass-hamburg]

@tgorochowik I tested it successful on my arty