or1200-generic: verilator: add top_module param

In section verilator top_module in now mandatory for the
simulated system/core.

Signed-off-by: Franck Jullien <franck.jullien@gmail.com>
or1200-generic: Regenerate wb_intercon

wb_intercon_gen now adds a wb_data_resize block for 8 bit slaves
Note though that this isn't completely automatic, so port width has
to be changed manually in the generated RTL
wb_intercon: Small wb_intercon_gen fixes
or1200-generic: update verilator support

This patch removes the local copy of elf-loader in or1200-generic.
This copy is no longer needed because fusesoc now adds verilator
files from all cores.

The verilator testbench is also cleaned-up and adapted to the
up-to-date elf-loader.

Signed-off-by: Franck Jullien <franck.jullien@gmail.com>