add support for vivado xsim and fusesoc

[skokvermon]

to run vivado xsim target with fusesoc, first install fusesoc, then

mkdir fusesoc
cd fusesoc
fusesoc library add axi git@github.com:skokvermon/axi.git
fusesoc library add common_cells git@github.com:skokvermon/common_cells.git
fusesoc library add common_verification git@github.com:skokvermon/common_verification.git
fusesoc core list
fusesoc run --tool xsim --target sim --no-export pulp-platform.org::axi:0.35.2.dev

[skokvermon]

@andreaskurth Please note that fusesoc doesn't support "-" in version number.
"-dev" version suffix must be replaced with ".dev"

[hossein1387]

Any plan on when this PR will be merged?

[micprog]

requires pulp-platform/common_verification#4

[thommythomaso]

Will be implemented in #262. Closed.

[skokvermon]

#262 is not working because of wrong ifdef XSIM