This PR introduces some major features while also changing the project structure to be more flexible
for multiple platforms (e.g. host tooling).
Added features:
1. Pure Rust FSBL for the Zedboard. This first variant is simplistic. It
is currently only capable of QSPI boot. It searches for a bitstream
and ELF file inside the boot binary, flashes them and jumps to them.
2. DDR, QSPI, private CPU timer modules
3. Tooling to auto-generate board specific DDR and DDRIOB config
parameters from the vendor provided ps7init.tcl file
Changed project structure:
1. All target specific project are inside a dedicated workspace inside
the `zynq` folder now.
2. All tool intended to be run on a host are inside a `tools` workspace
3. All other common projects are at the project root
