cappuccino/fetch: initialize imem_err during reset

Without this, during simulations, ibus_adr_o is undefined
after reset is released. This undefined state can lead
to an undefined state on ibus_err_i and we are stuck in
this state.

Signed-off-by: Franck Jullien <franck.jullien@gmail.com>
icache: reorganize OPTION_ICACHE_WAYS == 2 guard

When OPTION_ICACHE_WAYS == 1, code inside the
OPTION_ICACHE_WAYS == 2 guard contains references to out of
boundary indecies in vectors.
icarus can figure out that this code is not used, if the
OPTION_ICACHE_WAYS == 2 statement is on its own.
There are still problems with verilator, but that needs
a lot more work to fix.