verilator: add src_root in included dirs
verilator: add src_root in included dirs

Signed-off-by: Franck Jullien <7ddcd52d897de62c0010070b24d1f61cf69e2d93@gmail.com>

lowRISC/fusesoc,lowRISC/fusesoc,olofk/fusesoc,olofk/fusesoc